When was NATO founded?

NATO has added new members seven times since its founding in 1949, and since 2017 NATO has had 29 members. Twelve countries were part of the founding of NATO: Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the United Kingdom, and the United States. In 1952, Greece and Turkey became members of the Alliance, joined later by West Germany (in 1955) and Spain (in 1982). In 1990, with the reunification of Germany, NATO grew to include the former country of East Germany. Between 1994 and 1997, wider forums for regional cooperation between NATO and its neighbors were set up, including the Partnership for Peace, the Mediterranean Dialogue initiative and the Euro-Atlantic Partnership Council. In 1997, three former Warsaw Pact countries, Hungary, the Czech Republic, and Poland, were invited to join NATO. After this fourth enlargement in 1999, the Vilnius group of the Baltics and seven East European countries formed in May 2000 to cooperate and lobby for further NATO membership. Seven of these countries joined in the fifth enlargement in 2004. The Adriatic States Albania and Croatia joined in the sixth enlargement in 2009, Montenegro in 2017.

Member states of NATO

NATO (the North Atlantic Treaty Organization) is an international alliance that consists of 29 member states from North America and Europe. It was established at the signing of the North Atlantic Treaty on 4 April 1949. Article Five of the treaty states that if an armed attack occurs against one of the member states, it shall be considered an attack against all members, and other members shall assist the attacked member, with armed forces if necessary.

Of the 29 member countries, two are located in North America (Canada and the United States), 27 are in Europe, and one is in Eurasia (Turkey). All members have militaries, except for Iceland which does not have a typical army (but does, however, have a coast guard and a small unit of civilian specialists for NATO operations). Three of NATO's members are nuclear weapons states: France, the United Kingdom, and the United States. NATO has 12 original founding member nation states, and from 18 February 1952 to 6 May 1955, it added three more member nations, and a fourth on 30 May 1982. After the end of the Cold War, NATO added 13 more member nations (10 former Warsaw Pact members and three former Yugoslav republics) from 12 March 1999 to 5 June 2017.

United States President Donald Trump expressed interest in withdrawing from the organization during his 2016 presidential campaign, and only later stated the United States would protect allies in the event that Article V is invoked.

"The following list is sourced from the 2018 edition of "The Military Balance" published annually by the International Institute for Strategic Studies."

The United States has a larger defense expenditure than all other members combined. Criticism of the organization by then newly elected US President Donald Trump caused various reactions from American and European political figures, ranging from ridicule to panic. Pew Research Center's 2016 survey among its member states showed that while most countries viewed NATO positively, most NATO members preferred keeping their military spending the same. The response to whether their country should militarily aid another NATO country if it were to get into a serious military conflict with Russia was also mixed. Only in the US and Canada did more than 50% of the people answer that they should.

Population data from "CIA World Factbook"GDP data from IMFExpenditure data (except Iceland) from SIPRI Military Expenditure Database, Icelandic data (2013) from Statistics IcelandMilitary personnel data from NATO Iceland has no armed forces. 2015 data.

After its formation in 1949 with twelve founding members, NATO grew by including Greece and Turkey in 1952 and West Germany in 1955, and then later Spain in 1982. After the Cold War ended, and Germany reunited in 1990, there was a debate in NATO about continued expansion eastward. In 1999, Poland, Hungary, and the Czech Republic joined the organization, amid much debate within the organization and Russian opposition. Another expansion came with the accession of seven Central and Eastern European countries: Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia, and Slovenia. These nations were first invited to start talks of membership during the 2002 Prague summit, and joined NATO shortly before the 2004 Istanbul summit. Albania and Croatia joined on 1 April 2009, prior to the 2009 Strasbourg–Kehl summit. The most recent member state to be added to NATO is Montenegro on 5 June 2017.

Enlargement of NATO

Enlargement of the North Atlantic Treaty Organization (NATO) is the process of including new member states in NATO. NATO is a military alliance of twenty-seven European and two North American countries that constitutes a system of collective defense. The process of joining the alliance is governed by Article 10 of the North Atlantic Treaty, which allows only for the invitation of "other European States", and by subsequent agreements. Countries wishing to join have to meet certain requirements and complete a multi-step process involving political dialogue and military integration. The accession process is overseen by the North Atlantic Council, NATO's governing body.

As of 2018, NATO officially recognizes four aspiring members: Bosnia and Herzegovina, Georgia, Macedonia and Ukraine. The Federation of Bosnia and Herzegovina within Bosnia and Herzegovina has expressed willingness to join NATO, however, it faces consistent political pressure from Republika Srpska, the other political entity in the country, alongside its partners in Moscow. Macedonia has been prevented from joining the alliance by Greece, one effect of the Macedonian naming dispute. Future expansion is currently a topic of debate in several countries outside the alliance, and countries like Sweden, Finland, and Serbia have open political debate on the topic of membership, while in countries like Ukraine, support and opposition to membership is tied to ethnic and nationalist ideologies. The incorporation of countries formerly part of the Eastern Bloc and the Soviet Union has been a cause of increased tension between NATO countries and Russia.

NATO has added new members seven times since its founding in 1949 to include twenty-nine members. Twelve countries were part of the founding of NATO: Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the United Kingdom, and the United States. The early years of the Cold War saw a stark divide between Capitalist states, backed by United States, and Communist satellite states of the Soviet Union. This divide eased inclusion of Portugal under Salazar in NATO and encouraged the anti-Communist governments of Greece and Turkey to join NATO in 1952. Greece would suspend its membership in 1974, over the Turkish invasion of Cyprus, but rejoined in 1980 with Turkey's cooperation.

The Bonn–Paris conventions ended the allies’ occupation of West Germany, and were ratified in part on the condition that West Germany join NATO, which it did in 1955. Though initially isolationist, Spain under Francisco Franco was staunchly anti-Communist, and bound by regular defence agreements with NATO countries. After its transition to democracy, Spain came under pressure to normalize its European relations, including joining NATO, which it did in 1982. A referendum in 1986 confirmed popular support for this.

The first post-Cold War expansion of NATO came with German reunification on 1990, when the former East Germany became part of the Federal Republic of Germany and the alliance. This had been agreed in the Two Plus Four Treaty earlier in the year. To secure Soviet approval of a united Germany remaining in NATO, it was agreed that foreign troops and nuclear weapons would not be stationed in the former East Germany, and the topic of further NATO expansion east was raised.

There is no mention of NATO enlargement in the September–October 1990 agreements on German reunification, so there was no "formal commitment" not to expand. Whether or not the West "informally committed" to not enlarge NATO to the East is a matter of dispute among historians and international relations scholars. Harvard University historian Mark Kramer rejects that an informal agreement existed, whereas Texas A&M University political scientist Joshua R. Itzkowitz Shifrinson argues that an informal agreement existed. In December 2017, Svetlana Savranskaya and Tom Blanton of the National Security Archive at George Washington University argued that newly declassified documents showed that an informal agreement existed.

Jack Matlock, US ambassador to the Soviet Union during its final years, said that the West gave a "clear commitment" not to expand, and declassified documents indicate that Soviet negotiators were given the oral impression by diplomats like Hans-Dietrich Genscher and James Baker that NATO membership was off the table for countries such as Czechoslovakia, Hungary, or Poland. In 1996, Gorbachev wrote in his "Memoirs", that "during the negotiations on the unification of Germany they gave assurances that NATO would not extend its zone of operation to the east," and repeated this view in an interview in 2008. However, in 2014, Gorbachev said "The topic of 'NATO expansion' was not discussed at all [in 1990], and it wasn't brought up in those years. I say this with full responsibility. Western leaders didn't bring it up, either." Eduard Shevardnadze, foreign minister of the Soviet Union between 1985 and 1991, has always maintained that "NATO's expansion beyond German borders never came up for negotiation." According to Robert Zoellick, a State Department official involved in the Two Plus Four negotiating process, no formal commitment regarding enlargement was made.

In February 1991, Poland, Hungary, and the Czech Republic and Slovakia (as Czechoslovakia) formed the Visegrád Group to push for European integration under the European Union and NATO, as well as to conduct military reforms in line with NATO standards. Internal NATO reaction to these former Warsaw Pact countries was initially negative, but by the 1991 Rome summit in November, members agreed to a series of goals that could lead to accession, such as market and democratic liberalization, and that NATO should be a partner in these efforts. In subsequent years, wider forums for regional cooperation between NATO and its eastern neighbors were set up, including the North Atlantic Cooperation Council (later the Euro-Atlantic Partnership Council) and the Partnership for Peace.

While the other Visegrád members were invited to join NATO at its 1997 Madrid summit, Slovakia was excluded based on what several members considered undemocratic actions by nationalist Prime Minister Vladimír Mečiar. Romania and Slovenia were both considered for invitation in 1997, and each had the backing of a prominent NATO member, France and Italy respectively, but support for enlargement was not unanimous, particularly in the US Congress. In an open letter to US President Bill Clinton, more than forty foreign policy experts including Bill Bradley, Sam Nunn, Gary Hart, Paul Nitze, and Robert McNamara expressed their concerns about NATO expansion as both expensive and unnecessary given the lack of an external threat from Russia at that time.

A 2006 study in the journal "Security Studies" argued that the NATO enlargements in 1999 and 2004 contributed to democratic consolidation in Central and Eastern Europe.

Domestic politics in Eastern European countries continued to push for more enlargement, and political parties reluctant to move on NATO membership, such as the Bulgarian Socialist Party and Slovak HZDS, were voted out of office. Hungary's interest in joining was confirmed by a November 1997 referendum that returned 85.3 percent in favor of membership. Russia's actions in the First Chechen War were also a motivating factor for several countries that had memories of similar Soviet offensives.

At the 1999 Washington summit, where Hungary, Poland, and the Czech Republic officially joined, NATO also issued new guidelines for membership with individualized "Membership Action Plans" for Albania, Bulgaria, Estonia, Latvia, Lithuania, Macedonia, Romania, Slovakia, and Slovenia. In May 2000, these countries joined with Croatia to form the Vilnius Group in order to cooperate and lobby for common NATO membership, and by the 2002 Prague summit seven were invited for membership, which took place at the 2004 Istanbul summit. Russia was particularly upset with the addition of the three Baltic states, the first countries that were part of the Soviet Union to join NATO.

Croatia also started a Membership Action Plan at the 2002 summit, leading to a national debate on whether a referendum on NATO membership needed to be held there. Croatian Prime Minister Ivo Sanader ultimately agreed in January 2008, as part of forming a coalition government with the HSS and HSLS parties, not to officially propose one. Montenegro declared independence on 3 June 2006, and the new country subsequently joined the Partnership for Peace programme at the 2006 Riga summit. Albania and Croatia were invited to join NATO at the 2008 Bucharest summit that April, though Slovenia threatened to hold up Croatian membership over their border dispute in the Bay of Piran. Slovenia did ratify Croatia's accession protocol in February 2009, and Croatia and Albania both officially joined NATO just prior to the 2009 Strasbourg–Kehl summit, with little opposition from Russia.

Montenegro applied for a Membership Action Plan on 5 November 2008, which was granted in December 2009. Montenegro also began full membership with the Adriatic Charter of NATO aspirants in May 2009. On December 2, 2015, NATO formally invited Montenegro to join the alliance, with negotiations concluding in May 2016. Montenegro formally joined NATO on 5 June 2017.

The North Atlantic Treaty is the basis of the organization and as such, any changes including new membership requires ratification by all current signers of the treaty. The treaty's Article 10 describes how non-member states may join NATO, and outlines NATO's "open door" policy:

This article poses two general limits to non-member states. First, only European states are eligible for new membership, and second, these states not only need the approval of all the existing member states, but every member state can put some criteria forward that have to be attained. In practice, NATO formulates a common set of criteria, but for instance Greece blocks the Republic of Macedonia's accession to NATO, due to the disagreement over the use of the name Macedonia. Turkey similarly opposes the participation of the Republic of Cyprus with NATO institutions as long as the Cyprus dispute is not resolved.

Since the 1991 Rome summit, when the delegations of its member states officially offered cooperation with Europe's newly democratic states, NATO has addressed and further defined the expectations and procedure for adding new members. The 1994 Brussels Declaration reaffirmed the principles in Article 10 and led to the "Study on NATO Enlargement". Published in September 1995, the study outlined the "how and why" of possible enlargement in Europe, highlighting three principles from the 1949 treaty for members to have: "democracy, individual liberty, and rule of law".

As NATO Secretary General Willy Claes noted, the 1995 study did not specify the "who or when," though it discussed how the then newly formed Partnership for Peace and North Atlantic Cooperation Council could assist in the enlargement process, and noted that on-going territorial disputes could be an issue for whether a country was invited. At the 1997 Madrid summit, the heads of state of NATO issued the "Madrid Declaration on Euro-Atlantic Security and Cooperation" which invited three Eastern European countries to join the alliance, out of the twelve that had at that point requested to join, laying out a path for others to follow.

The biggest step in the formalization of the process for inviting new members came at the 1999 Washington summit when the Membership Action Plan (MAP) mechanism was approved as a stage for the current members to regularly review the formal applications of aspiring members. A country's participation in MAP entails the annual presentation of reports concerning its progress on five different measures:

NATO provides feedback as well as technical advice to each country and evaluates its progress on an individual basis. Once a country is agreed to meet the requirements, NATO can issue that country an invitation to begin accession talks. Currently, two countries have a Membership Action Plan: Bosnia and Herzegovina and Macedonia. Former MAP participants were Albania and Croatia between May 2002 and April 2009, and Montenegro between December 2009 and June 2017, when they joined NATO. The final accession process, once invited, involves five steps leading up to the signing of the accession protocols and the acceptance and ratification of those protocols by the governments of the current NATO members.

Intensified Dialogue was first introduced in April 2005 at an informal meeting of foreign ministers in Vilnius, Lithuania, as a response to Ukrainian aspirations for NATO membership and related reforms taking place under President Viktor Yushchenko, and which followed the 2002 signing of the NATO–Ukraine Action Plan under his predecessor, Leonid Kuchma. This formula, which includes discussion of a "full range of political, military, financial and security issues relating to possible NATO membership" had its roots in the 1997 Madrid summit, where the participants had agreed "to continue the Alliance's intensified dialogues with those nations that aspire to NATO membership or that otherwise with to pursue a dialogue with NATO on membership questions".

In September 2006, Georgia became the second to be offered the Intensified Dialogue status, following a rapid change in foreign policy under President Mikheil Saakashvili, and what they perceived as a demonstration of military readiness during the 2006 Kodori crisis. Montenegro, Bosnia and Herzegovina, and Serbia similarly received offers at the April 2008 Bucharest summit. While their neighbors both requested and accepted the dialogue programme, Serbia's offer was presented to guarantee the possibility of future ties with the alliance.

Macedonia and Bosnia and Herzegovina are currently the only countries with a Membership Action Plan, and together with Georgia, were named NATO "aspirant countries" at the North Atlantic Council meeting on 7 December 2011. In 2008, Greece blocked an invitation to its northern neighbor, pending resolution of the Macedonia naming dispute. Macedonia was part of the Vilnius Group, and had formed the Adriatic Charter with Croatia and Albania in 2003 to better coordinate NATO accession. Ukraine was recognized as an aspirant country after the 2014 Ukrainian revolution.

The 1995 NATO bombing of Bosnia and Herzegovina targeted the Bosnian Serb Army and together with international pressure led to the resolution of the Bosnian War and the signing of the Dayton Agreement in 1995. Since then, NATO has led the Implementation Force and Stabilization Force, and other peacekeeping efforts in the country. Bosnia and Herzegovina joined the Partnership for Peace in 2006, and signed an agreement on security cooperation in March 2007.

Bosnia and Herzegovina began further cooperation with NATO within their Individual Partnership Action Plan in January 2008. The country then started the process of Intensified Dialogue at the 2008 Bucharest summit. The country was invited to join the Adriatic Charter of NATO aspirants in September 2008. On 2 October 2009, Haris Silajdžić, the Bosniak Member of the Presidency, announced official application for Membership Action Plan. On 22 April 2010, NATO agreed to launch the Membership Action Plan for Bosnia and Herzegovina, but with certain conditions attached. Turkey is thought to be the biggest supporter of Bosnian membership, and heavily influenced the decision.

The conditions of the MAP, however, stipulated that no Annual National Programme could be launched until 63 military facilities are transferred from Bosnia's political divisions to the central government, which is one of the conditions for the OHR closure. The leadership of the Republika Srpska has opposed this transfer as a loss of autonomy. All movable property, including all weapons and other army equipment, is fully registered as the property of the country starting 1 January 2006. A ruling of the Constitutional Court of Bosnia and Herzegovina on 6 August 2017 decided that a disputed military facility in Han Pijesak is to be registered as property of Bosnia and Herzegovina. It is expected to be a precedent for all other similar facilities, and could thus be the final factor that will enable the activation of the MAP for Bosnia. Despite that all immovable property is not fully registered, NATO approved the activation of the Membership Action Plan for Bosnia and Herzegovina, and called on Bosnia to submit an Annual National Program on 5 December 2018.

An August 2010 poll showed that 70 percent of the country supports NATO membership, but results were very different in the two constituent entities. While 90 percent of the Federation of Bosnia and Herzegovina supported NATO membership, only 33 percent in Republika Srpska did.

Bosnia's chances of joining NATO may depend on Serbia's attitude towards the alliance, since the leadership of Republika Srpska might be reluctant to go against Serbian interests. In October 2017, the National Assembly of the Republika Srpska passed a nonbinding resolution opposing NATO membership for Bosnia and Herzegovina.

Georgia moved quickly following the Rose Revolution in 2003 to seek closer ties with NATO. Georgia's northern neighbor, Russia, opposed the closer ties, including those expressed at the 2008 Bucharest summit where NATO members promised that Georgia would eventually join the organization.

Complications in the relationship between NATO and Georgia includes presence of Russian forces in internationally recognized Georgian territory as a result of multiple recent conflicts, like the 2008 Russo-Georgian War, over the territories of Abkhazia and South Ossetia, both of which are home to a large number of citizens of the Russian Federation. On 21 November 2011, Russian President Dmitry Medvedev while addressing soldiers in Vladikavkaz near the Georgian border stated that the 2008 invasion had prevented any further NATO enlargement into the former Soviet sphere.

A nonbinding referendum in 2008 resulted in 72.5 percent of voters supporting NATO accession. In May 2013, Georgian Prime Minister Bidzina Ivanishvili stated that his goal is to get a Membership Action Plan (MAP) for his country from NATO in 2014. In June 2014, diplomats from NATO suggested that while a MAP was unlikely, a package of "reinforced cooperation" agreements was a possible compromise. Anders Fogh Rasmussen confirmed that this could include the building of military capabilities and armed forces training.

Macedonia is recognized under the name The Former Yugoslav Republic of Macedonia by NATO, though they note that Turkey recognizes the name Macedonia. The country joined the Partnership for Peace in 1995, and commenced its Membership Action Plan in 1999, at the same time as Albania. Participating in the 1999 NATO intervention in Kosovo, it received aid from NATO in dealing with refugees fleeing from Kosovo. In August 2001, NATO intervened in the 2001 insurgency, during which a rebel Albanian group, the National Liberation Army, fought government forces. In Operation Essential Harvest, NATO troops joined with the Macedonian military to disarm rebel forces following a cease-fire agreement.

At the 2008 Bucharest summit, Greece blocked a proposed invitation because it believed that its neighbor's constitutional name implies territorial aspirations toward its own region of Greek Macedonia. NATO nations agreed that the country would receive an invitation upon resolution of the Macedonia naming dispute. Macedonia sued Greece at the International Court of Justice (ICJ) over their veto of Macedonia's NATO membership. The ICJ ruled in December 2011 that Greece was wrong to have blocked its neighbor's bid, finding them in breach of a 1995 interim accord that allowed Macedonia to join international organizations under the name "the Former Yugoslav Republic of Macedonia", which is how NATO, with the exception of Turkey, recognizes their bid. Greece also blocks Macedonia's accession to the European Union over the naming dispute. In March 2016, Macedonian Defense Minister Zoran Jolevski stated his hope that his country's handling of the European migrant crisis might bring it closer to NATO membership.

A poll following the 2008 summit showed that 82.5 percent of citizens surveyed opposed changing the constitutional name in order to join NATO. Elections were called following the 2008 summit, resulting in further support for the centre-right pro-NATO party, VMRO-DPMNE. The elections were marred by violence that was criticized by NATO members. Ethnic tensions have persisted in Macedonia, and NATO has called for dialogue following clashes such as those in the city of Kumanovo in 2015, which were blamed in part on the delay in NATO and European integration. NATO membership in general is supported by 81 percent according to a November 2014 poll. On 12 June 2017, Prime Minister Zoran Zaev signaled that he will consider alternatives names for the country in order to strike a compromise with Greece, settle the naming dispute, and lift Greek objections to Macedonia joining the alliance. Zaev also floated the idea of Macedonia joining the alliance under the provisional name it uses at the United Nations. After the Prespa Agreement was reached in June 2018, NATO invited Macedonia to begin membership talks on 11 July 2018, saying the country could join the organization once the naming issue was resolved. Formal accession talks began on 18 October 2018.

Ukraine's present and future relationship with NATO has been politically divisive, and is part of a larger debate between Ukraine's political and cultural ties to both the European Union and Russia. It established ties to the alliance with a NATO–Ukraine Action Plan on 22 November 2002, and joined NATO's Partnership for Peace initiative in February 2005. Then in April 2005, Ukraine entered into the Intensified Dialogue programme with NATO.

In March 2008, under Ukrainian President Viktor Yushchenko and Prime Minister Yulia Tymoshenko, Ukraine sent an official letter of application for a Membership Action Plan (MAP), the first step in joining NATO. These leaders however guaranteed their opposition that membership in any military alliance would not pass without public approval in a referendum. This idea had gained support from a number of NATO leaders, particularly those in Central and Eastern Europe. Russian leaders like Prime Minister and President-Elect Dmitry Medvedev made clear their opposition to Ukraine membership, and leading up to the April 2008 Bucharest summit their emissary actively lobbied against a Ukrainian MAP. After some debate among members at the summit, NATO Secretary General Jaap de Hoop Scheffer declared in a press conference that Ukraine, together with Georgia, would someday join NATO, but neither would begin Membership Action Plans. At this summit, Russian President Vladimir Putin, in his last international speech before switching jobs with Medvedev, listed his grievances with NATO, and called Ukrainian membership "a direct threat" to his country.
The 2010 election returned Viktor Yanukovych to the presidency and marked a turnaround in Ukraine's relations with NATO. In February 2010, he stated that Ukraine's relations with NATO were currently "well-defined", and that there was "no question of Ukraine joining NATO". He said the issue of Ukrainian membership of NATO might "emerge at some point, but we will not see it in the immediate future". While visiting Brussels in March 2010, he further stated that there would be no change to Ukraine's status as a member of the alliance's outreach programme. He later reiterated during a trip to Moscow that Ukraine would remain a "European, non-aligned state". Then, on 3 June 2010 the Ukrainian parliament voted to exclude the goal of "integration into Euro-Atlantic security and NATO membership" from the country's national security strategy in a bill drafted by Yanukovych himself. The bill forbade Ukraine's membership in any military bloc, but allowed for co-operation with alliances such as NATO.

Following months of Euromaidan street protests that began because of his refusal to sign an Association Agreement with the European Union in favor of deals from Russia, President Yanukovych fled Kyiv in February 2014, ultimately to Russia, and parliament voted to remove him from his post. This brought another change in direction of Ukraine's association with Europe and by extension NATO. In 2014, pro-Russian unrest occurred in eastern Ukraine and Crimea was annexed by the Russian Federation in March. As part of an effort to assuage concerned groups, newly installed Prime Minister Arseniy Yatsenyuk addressed the topic in a speech on 18 March 2014, emphasizing that Ukraine was not seeking NATO membership. US President Barack Obama echoed this position the following week, while calling for greater NATO presence in Eastern Europe.

However, in response to the Russian military intervention in Ukraine, Yatsenyuk announced his intentions to resume the bid for NATO integration on 29 August 2014, and in December 2014, Ukraine's parliament voted to drop the non-aligned status that it adopted in 2010. NATO Secretary General Anders Fogh Rasmussen has stated that NATO membership is still an option for Ukraine, and support for NATO membership has risen to 63.9 percent in government-controlled Ukraine according to a July 2015 poll. Previous polls had shown that the decline in opposition to membership was linked to the ongoing Russian intervention.

On 8 June 2017, Ukraine's Verkhovna Rada passed a law making integration with NATO a foreign policy priority. In July 2017 Poroshenko announced that he would seek the opening of negotiations on a Membership Action Plan with NATO.

By March 2018, NATO had recognized Ukraine as an aspirant country.

On September 20, 2018, the Ukrainian parliament approved amendments to the constitution that would make the accession of the country to NATO and the EU a central goal and the main foreign policy objective.

Finland participates in nearly all sub-areas of the Partnership for Peace programme, and has provided peacekeeping forces to both the Afghanistan and Kosovo missions. The possibility of Finland's membership in NATO was one of the most important issues debated in relation to the Finnish presidential election of 2006, and continues to be a significant issue in Finnish politics. In 2007, Finland made various technical preparations for membership, with the then Defence Minister Jyri Häkämies eager to pursue NATO membership. Nevertheless, public interest in the issue has since decreased. In April 2014, the government announced that they would sign a "Memorandum of Understanding" with NATO on Finland's readiness to receive military assistance and to aid NATO in equipment maintenance. However, Defence Minister Carl Haglund emphasized that this memorandum would not be a step towards membership.

Out of the major Finnish political parties, the National Coalition Party and Swedish People's Party of Finland support NATO membership. In 2016, the party conference of the National Coalition Party agreed that Finland should apply for membership in the "following years". In the vision of the Swedish People's Party of Finland, Finland will be a NATO member in 2025. Many individual politicians have advocated for NATO as well, including the current President Sauli Niinistö and former Prime Minister Alexander Stubb, as well as former President Martti Ahtisaari, who has argued that Finland should join all the organizations supported by other Western democracies in order "to shrug off once and for all the burden of Finlandization." Two other former presidents from the Social Democratic Party, Tarja Halonen and Mauno Koivisto, have publicly opposed the idea, arguing that NATO membership would deteriorate Finland's relations with Russia.

Finland has received some very critical feedback from Russia for even considering the possibility of joining NATO, with a 2009 study suggesting this could have repercussions for Russia's relations with the EU and NATO as a whole. Following the 2008 Russo-Georgian War, Finnish Prime Minister Matti Vanhanen reiterated that Finland had no plans to join NATO, and stated that the main lesson of the war was the need for closer ties to Russia. In a June 2014 interview in the Finnish newspaper "Hufvudstadsbladet", Vladimir Putin's personal envoy Sergey Alexandrovich Markov accused Finland of extreme "Russophobia" and suggested that Finland joining NATO could start World War III. In July 2016, Putin stated on a visit to Finland, that Russia would increase the number of troops on the Finnish border if Finland were to join NATO. He also warned that NATO would "fight to the last Finn against Russia".

A survey conducted by Finnish pollster EVA in January 2015 found that 43 percent of Finns polled opposed NATO membership, while 26 percent supported and 32 percent were undecided. EVA has noted a downward trend in the percent opposed that started in 1998, including a steep decline after the 2012 presidential election. In March 2014, during Russia's annexation of Crimea, one survey showed only 22 percent supported membership, though a second showed that 53 percent would support membership if Finnish leadership recommended it. Support for a military alliance with neighbor Sweden was also high, at 54 percent, and Finland could possibly seek an enlarged role for NORDEFCO. Finnish Minister of Defence Carl Haglund suggested that a referendum on NATO membership could be held sometime after the 2015 parliamentary election. The newest poll from October 2017 showed that support for membership remained at 22%, while rising to 33% in the suggested scenario in which Sweden would join.

Ireland has been a member of NATO's Partnership for Peace (PfP) programme and Euro-Atlantic Partnership Council (EAPC) since 1999, but has not applied to join NATO as a member state due to its traditional policy of military neutrality. Ireland participates in the alliance's PfP Planning and Review Process (PARP), which aims to increase the interoperability of the Irish military, the Defence Forces, with other NATO member states and bring them into line with accepted international standards so as to successfully deploy with other professional military forces on peacekeeping operations overseas. Ireland supplied a small number of troops to the NATO-led International Security Assistance Force (ISAF) in Afghanistan (2001–2014) and supports the ongoing NATO-led Kosovo Force (KFOR).

Currently no major political party in Ireland fully supports ascension into NATO, a reflection on public and media opinion in the country. There are a number of politicians who support Ireland joining NATO, mainly within the centre-right Fine Gael party, but the majority of politicians still do not. It is widely understood that a referendum would have to be held before any changes could be made to neutrality or to joining NATO. Former Secretary General of NATO Anders Fogh Rasmussen said during a visit to the country in 2013 that the "door is open" for Ireland to join NATO at any time.

Moldova's constitution forbids the country from joining a military alliance, but some politicians, such as Moldovan Minister of Defence Vitalie Marinuța, have suggested joining NATO as part of a larger European integration. Moldova joined NATO's Partnership for Peace in 1994, and initiated an Individual Partnership Action Plan in 2010. Following the 2014 annexation of Crimea by Russia, NATO officials warned that Russia might seek to annex Transnistria, a breakaway Moldovan region. This separatist issue could preclude Moldova from joining NATO.

The NATO intervention in Bosnia and Herzegovina in 1992 and the NATO bombing of Yugoslavia in 1999 resulted in strained relations between Serbia and NATO. Relations were further strained following Kosovo's declaration of independence in 2008 while a protectorate of the United Nations with security support from NATO. However, Serbia was invited and joined the Partnership for Peace programme during the 2006 Riga summit and in 2008, was invited to enter the intensified dialogue programme whenever the country is ready.

Serbia's Parliament passed a resolution in 2007 which declared their military neutrality until such time as a referendum was held on the issue. On 1 October 2008, Serbian Defence Minister Dragan Šutanovac signed the Information Exchange Agreement with NATO, one of the prerequisites for fuller membership in the Partnership for Peace programme. In April 2011 Serbia's request for an IPAP was approved by NATO, and Serbia submitted a draft IPAP in May 2013. The agreement was finalized on 15 January 2015.

A CeSID poll in June 2015 conducted with the support of the United States Agency for International Development (USAID) indicated that only 12 percent of those polled supported for NATO membership, down from 25 percent in 2012, and 73 percent were opposed. The minor Liberal Democratic Party and Serbian Renewal Movement remain the most vocal political parties in favor of NATO membership. Although Serbia aspires to join the European Union, Serbia may seek to maintain military neutrality, joining neither NATO nor the Collective Security Treaty Organization (CSTO).

In 1949 Sweden chose not to join NATO and declared a security policy aiming for non-alignment in peace and neutrality in war. A modified version now qualifies non-alignment in peace for possible neutrality in war. This position was maintained without much discussion during the Cold War. Since the 1990s however there has been an active debate in Sweden on the question of NATO membership in the post–Cold War world. These ideological divides were visible in November 2006 when Sweden could either buy two new transport planes or join NATO's plane pool, and in December 2006, when Sweden was invited to join the NATO Response Force. Sweden have been active participants in NATO-led missions in Bosnia (IFOR and SFOR), Kosovo (KFOR), Afghanistan (ISAF), and Libya (Operation Unified Protector).

The ruling Swedish Social Democratic Party have remained in favour of neutrality and non-alignment. This preference is shared by their partners, the Green Party, as well as the Left Party. The centre-right Moderate Party and the Liberal Party are the largest parties by current parliamentary representation in favor of NATO membership. The 2014 Russian annexation of Crimea is credited with renewed public calls for NATO membership from notable politicians. The Centre Party was opposed to NATO membership until September 2015, when party leadership under Annie Lööf announced that they would motion to change the party policy in order to push for Sweden to join NATO at their next party conference. The Christian Democrats, also previously opposed, likewise voted to support NATO membership at their party meeting on 9 October 2015.

Polling has shown a rise in support for NATO membership among Swedes since 2008 according to Ipsos polling, going from 22 percent in May 2008 to 33 percent in January 2015, with another from the SOM Institute in May 2015 showing similar numbers. According to "Svenska Dagbladet", support in 2011 was at 23 percent, and has risen somewhat significantly to 41 percent in September 2015, when only 39 percent of respondents were opposed to NATO membership. An October 2014 survey commissioned by TV4 News also showed slightly more respondents supporting membership than opposing it. In 2014, news that a military expert in Sweden had calculated that the country could hold out for a week if attacked temporarily lifted support for NATO membership in polls. A May 2017 poll by Pew showed that support for membership had risen to 47 percent.

Austria and Switzerland are both members of the Partnership for Peace, and border NATO member states. Malta is also a member of the Partnership for Peace and the European Union. However, each country has a long-standing policy of neutrality. Cyprus is the only Member state of the European Union that is not a member of the Partnership for Peace, with any treaty blocked by Turkey's concerns regarding the Cyprus dispute. According to Minister of Foreign Affairs Enver Hoxhaj, integration with NATO is a priority for Kosovo, which declared independence from Serbia in 2008. Hoxhaj stated in 2014 that the country's goal is to be a NATO member by 2022. However, four NATO member states, Greece, Romania, Spain, and Slovakia, do not recognize Kosovo's independence. United Nations membership, which Kosovo does not have, is considered to be necessary for NATO membership. In December 2018, the Kosovar Prime Minister Ramush Haradinaj stated that Kosovo will apply for NATO membership after the formation of the Kosovo Armed Forces.

Russia, Armenia, Belarus, and Kazakhstan are all members of the Collective Security Treaty Organization (CSTO), an alternative military alliance. In 2009, Russian envoy Dmitry Rogozin did not rule out joining NATO at some point, but stated that Russia was currently more interested in leading a coalition as a great power. Azerbaijan has committed to a policy of neutrality, but has not ruled out eventually joining NATO or the CSTO.

Christopher Sands of the Hudson Institute proposed Mexican membership of NATO in order to enhance NATO cooperation with Mexico and develop a "North American pillar" for regional security. In June 2013, Colombian President Juan Manuel Santos stated his hope that Colombia's cooperation with NATO could result in NATO membership, though his Foreign Minister, Juan Carlos Pinzon, quickly clarified that Colombia is not actively seeking NATO membership. Ivo Daalder and James Goldgeier proposed a "global NATO" that would incorporate democratic states from around the world, including Australia, New Zealand, Japan, South Korea, Brazil, South Africa, and India, while Republican presidential candidate Rudy Giuliani suggested expanding NATO to include Singapore, Israel, Australia, India, and Japan. Expanding NATO outside of Europe would require amending Article 10 of the North Atlantic Treaty.

The North Atlantic Treaty Organization (NATO ; ; '), also called the North Atlantic Alliance, is an intergovernmental military alliance between 29 North American and European countries. The organization implements the North Atlantic Treaty that was signed on 4 April 1949. NATO constitutes a system of collective defence whereby its independent member states agree to mutual defence in response to an attack by any external party. NATO’s Headquarters are located in Haren, Brussels, Belgium, while the headquarters of Allied Command Operations is near Mons, Belgium.

NATO

Since its founding, the admission of new member states has increased the alliance from the original 12 countries to 29. The most recent member state to be added to NATO is Montenegro on 5 June 2017. NATO currently recognizes Bosnia and Herzegovina, Georgia, Macedonia and Ukraine as aspiring members. An additional 21 countries participate in NATO's Partnership for Peace program, with 15 other countries involved in institutionalized dialogue programs. The combined military spending of all NATO members constitutes over 70% of the global total. Members have committed to reach or maintain defense spending of at least 2% of GDP by 2024.

On 4 March 1947 the Treaty of Dunkirk was signed by France and the United Kingdom as a "Treaty of Alliance and Mutual Assistance" in the event of a possible attack by Germany or the Soviet Union in the aftermath of World War II. In 1948, this alliance was expanded to include the Benelux countries, in the form of the Western Union, also referred to as the Brussels Treaty Organization (BTO), established by the Treaty of Brussels. Talks for a new military alliance which could also include North America resulted in the signature of the North Atlantic Treaty on 4 April 1949 by the member states of the Western Union plus the United States, Canada, Portugal, Italy, Norway, Denmark and Iceland.

The North Atlantic Treaty was largely dormant until the Korean War initiated the establishment of NATO to implement it, by means of an integrated military structure: This included the formation of Supreme Headquarters Allied Powers Europe (SHAPE) in 1951, which adopted the Western Union's military structures and plans. In 1952 the post of Secretary General of NATO was established as the organization's chief civilian, the first major NATO maritime exercises began; Exercise Mainbrace, and Greece and Turkey acceded. In 1955 West Germany was also incorporated into NATO, which resulted in the creation of the Soviet-dominated Warsaw Pact, delineating the two opposing sides of the Cold War.

Doubts over the strength of the relationship between the European states and the United States ebbed and flowed, along with doubts over the credibility of the NATO defense against a prospective Soviet invasion – doubts that led to the development of the independent French nuclear deterrent and the withdrawal of France from NATO's military structure in 1966. In 1982 the newly democratic Spain joined the alliance.

The collapse of the Warsaw Pact in 1989–1991 removed the "de facto" main adversary of NATO and caused a strategic re-evaluation of NATO's purpose, nature, tasks, and their focus on the continent of Europe. This shift started with the 1990 signing in Paris of the Treaty on Conventional Armed Forces in Europe between NATO and the Soviet Union, which mandated specific military reductions across the continent that continued after the dissolution of the Soviet Union in December 1991. At that time, European countries accounted for 34 percent of NATO's military spending; by 2012, this had fallen to 21 percent. NATO also began a gradual expansion to include newly autonomous Central and Eastern European nations, and extended its activities into political and humanitarian situations that had not formerly been NATO concerns.

After the fall of the Berlin Wall in Germany in 1989, the organization conducted its first military interventions in Bosnia from 1992 to 1995 and later Yugoslavia in 1999 during the breakup of Yugoslavia. Politically, the organization sought better relations with former Warsaw Pact countries, most of which joined the alliance in 1999 and 2004., requiring member states to come to the aid of any member state subject to an armed attack, was invoked for the first and only time after the September 11 attacks, after which troops were deployed to Afghanistan under the NATO-led ISAF. The organization has operated a range of additional roles since then, including sending trainers to Iraq, assisting in counter-piracy operations and in 2011 enforcing a no-fly zone over Libya in accordance with UN Security Council Resolution 1973. The less potent Article 4, which merely invokes consultation among NATO members, has been invoked five times following incidents in the Iraq War, Syrian Civil War, and annexation of Crimea.

The first post-Cold War expansion of NATO came with German reunification on 3 October 1990, when the former East Germany became part of the Federal Republic of Germany and the alliance. As part of post-Cold War restructuring, NATO's military structure was cut back and reorganized, with new forces such as the Headquarters Allied Command Europe Rapid Reaction Corps established. The changes brought about by the collapse of the Soviet Union on the military balance in Europe were recognized in the Adapted Conventional Armed Forces in Europe Treaty, which was signed in 1999. The policies of French President Nicolas Sarkozy resulted in a major reform of France's military position, culminating with the return to full membership on 4 April 2009, which also included France rejoining the NATO Military Command Structure, while maintaining an independent nuclear deterrent.

Between 1994 and 1997, wider forums for regional cooperation between NATO and its neighbors were set up, like the Partnership for Peace, the Mediterranean Dialogue initiative and the Euro-Atlantic Partnership Council. In 1998, the NATO–Russia Permanent Joint Council was established. Between 1999 and 2017 NATO incorporated the following Central and Eastern European countries, including several former communist states: the Czech Republic, Hungary, Poland, Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia, Slovenia, Albania, Croatia and Montenegro.

The Russian intervention in Crimea in 2014 lead to strong condemnation by NATO nations and the creation of a new "spearhead" force of 5,000 troops at bases in Estonia, Lithuania, Latvia, Poland, Romania, and Bulgaria. At the subsequent 2014 Wales summit, the leaders of NATO's member states formally committed for the first time spend the equivalent of at least 2% of their gross domestic products on defence by 2024, which had previously been only an informal guideline.

No military operations were conducted by NATO during the Cold War. Following the end of the Cold War, the first operations, "Anchor Guard" in 1990 and "Ace Guard" in 1991, were prompted by the Iraqi invasion of Kuwait. Airborne early warning aircraft were sent to provide coverage of southeastern Turkey, and later a quick-reaction force was deployed to the area.

The Bosnian War began in 1992, as a result of the breakup of Yugoslavia. The deteriorating situation led to United Nations Security Council Resolution 816 on 9 October 1992, ordering a no-fly zone over central Bosnia and Herzegovina, which NATO began enforcing on 12 April 1993 with Operation "Deny Flight". From June 1993 until October 1996, Operation "Sharp Guard" added maritime enforcement of the arms embargo and economic sanctions against the Federal Republic of Yugoslavia. On 28 February 1994, NATO took its first wartime action by shooting down four Bosnian Serb aircraft violating the no-fly zone.

On 10 and 11 April 1994, during the Bosnian War, the United Nations Protection Force called in air strikes to protect the Goražde safe area, resulting in the bombing of a Bosnian Serb military command outpost near Goražde by two US F-16 jets acting under NATO direction. This resulted in the taking of 150 U.N. personnel hostage on 14 April. On 16 April a British Sea Harrier was shot down over Goražde by Serb forces. A two-week NATO bombing campaign, Operation "Deliberate Force", began in August 1995 against the Army of the Republika Srpska, after the Srebrenica massacre.

NATO air strikes that year helped bring the Yugoslav wars to an end, resulting in the Dayton Agreement in November 1995. As part of this agreement, NATO deployed a UN-mandated peacekeeping force, under Operation "Joint Endeavor", named IFOR. Almost 60,000 NATO troops were joined by forces from non-NATO nations in this peacekeeping mission. This transitioned into the smaller SFOR, which started with 32,000 troops initially and ran from December 1996 until December 2004, when operations were then passed onto European Union Force Althea. Following the lead of its member nations, NATO began to award a service medal, the NATO Medal, for these operations.

In an effort to stop Slobodan Milošević's Serbian-led crackdown on KLA separatists and Albanian civilians in Kosovo, the United Nations Security Council passed Resolution 1199 on 23 September 1998 to demand a ceasefire. Negotiations under US Special Envoy Richard Holbrooke broke down on 23 March 1999, and he handed the matter to NATO, which started a 78-day bombing campaign on 24 March 1999. Operation "Allied Force" targeted the military capabilities of what was then the Federal Republic of Yugoslavia. During the crisis, NATO also deployed one of its international reaction forces, the ACE Mobile Force (Land), to Albania as the Albania Force (AFOR), to deliver humanitarian aid to refugees from Kosovo.

Though the campaign was criticized for high civilian casualties, including bombing of the Chinese embassy in Belgrade, Milošević finally accepted the terms of an international peace plan on 3 June 1999, ending the Kosovo War. On 11 June, Milošević further accepted UN resolution 1244, under the mandate of which NATO then helped establish the KFOR peacekeeping force. Nearly one million refugees had fled Kosovo, and part of KFOR's mandate was to protect the humanitarian missions, in addition to deterring violence. In August–September 2001, the alliance also mounted Operation "Essential Harvest", a mission disarming ethnic Albanian militias in the Republic of Macedonia., 4,882 KFOR soldiers, representing 31 countries, continue to operate in the area.

The US, the UK, and most other NATO countries opposed efforts to require the UN Security Council to approve NATO military strikes, such as the action against Serbia in 1999, while France and some others claimed that the alliance needed UN approval. The US/UK side claimed that this would undermine the authority of the alliance, and they noted that Russia and China would have exercised their Security Council vetoes to block the strike on Yugoslavia, and could do the same in future conflicts where NATO intervention was required, thus nullifying the entire potency and purpose of the organization. Recognizing the post-Cold War military environment, NATO adopted the Alliance Strategic Concept during its Washington summit in April 1999 that emphasized conflict prevention and crisis management.

The September 11 attacks in the United States caused NATO to invoke Article 5 of the NATO Charter for the first time in the organization's history. The Article says that an attack on any member shall be considered to be an attack on all. The invocation was confirmed on 4 October 2001 when NATO determined that the attacks were indeed eligible under the terms of the North Atlantic Treaty. The eight official actions taken by NATO in response to the attacks included Operation "Eagle Assist" and Operation "Active Endeavour", a naval operation in the Mediterranean Sea which is designed to prevent the movement of terrorists or weapons of mass destruction, as well as enhancing the security of shipping in general which began on 4 October 2001.

The alliance showed unity: On 16 April 2003, NATO agreed to take command of the International Security Assistance Force (ISAF), which includes troops from 42 countries. The decision came at the request of Germany and the Netherlands, the two nations leading ISAF at the time of the agreement, and all nineteen NATO ambassadors approved it unanimously. The handover of control to NATO took place on 11 August, and marked the first time in NATO's history that it took charge of a mission outside the north Atlantic area.

ISAF was initially charged with securing Kabul and surrounding areas from the Taliban, al Qaeda and factional warlords, so as to allow for the establishment of the Afghan Transitional Administration headed by Hamid Karzai. In October 2003, the UN Security Council authorized the expansion of the ISAF mission throughout Afghanistan, and ISAF subsequently expanded the mission in four main stages over the whole of the country.

On 31 July 2006, the ISAF additionally took over military operations in the south of Afghanistan from a US-led anti-terrorism coalition. Due to the intensity of the fighting in the south, in 2011 France allowed a squadron of Mirage 2000 fighter/attack aircraft to be moved into the area, to Kandahar, in order to reinforce the alliance's efforts. During its 2012 Chicago Summit, NATO endorsed a plan to end the Afghanistan war and to remove the NATO-led ISAF Forces by the end of December 2014. ISAF was disestablished in December 2014 and replaced by the follow-on training Resolute Support Mission

In August 2004, during the Iraq War, NATO formed the NATO Training Mission – Iraq, a training mission to assist the Iraqi security forces in conjunction with the US led MNF-I. The NATO Training Mission-Iraq (NTM-I) was established at the request of the Iraqi Interim Government under the provisions of United Nations Security Council Resolution 1546. The aim of NTM-I was to assist in the development of Iraqi security forces training structures and institutions so that Iraq can build an effective and sustainable capability that addresses the needs of the nation. NTM-I was not a combat mission but is a distinct mission, under the political control of NATO's North Atlantic Council. Its operational emphasis was on training and mentoring. The activities of the mission were coordinated with Iraqi authorities and the US-led Deputy Commanding General Advising and Training, who was also dual-hatted as the Commander of NTM-I. The mission officially concluded on 17 December 2011.

Turkey invoked the first Article 4 meetings in 2003 at the start of the Iraq War. Turkey also invoked this article twice in 2012 during the Syrian Civil War, after the downing of an unarmed Turkish F-4 reconnaissance jet, and after a mortar was fired at Turkey from Syria, and again in 2015 after threats by Islamic State of Iraq and the Levant to its territorial integrity.

Beginning on 17 August 2009, NATO deployed warships in an operation to protect maritime traffic in the Gulf of Aden and the Indian Ocean from Somali pirates, and help strengthen the navies and coast guards of regional states. The operation was approved by the North Atlantic Council and involves warships primarily from the United States though vessels from many other nations are also included. Operation "Ocean Shield" focuses on protecting the ships of Operation "Allied Provider" which are distributing aid as part of the World Food Programme mission in Somalia. Russia, China and South Korea have sent warships to participate in the activities as well. The operation seeks to dissuade and interrupt pirate attacks, protect vessels, and abetting to increase the general level of security in the region.

During the Libyan Civil War, violence between protestors and the Libyan government under Colonel Muammar Gaddafi escalated, and on 17 March 2011 led to the passage of United Nations Security Council Resolution 1973, which called for a ceasefire, and authorized military action to protect civilians. A coalition that included several NATO members began enforcing a no-fly zone over Libya shortly afterwards, beginning with Opération Harmattan by the French Air Force on March 19.

On 20 March 2011, NATO states agreed on enforcing an arms embargo against Libya with Operation "Unified Protector" using ships from NATO Standing Maritime Group 1 and Standing Mine Countermeasures Group 1, and additional ships and submarines from NATO members. They would "monitor, report and, if needed, interdict vessels suspected of carrying illegal arms or mercenaries".

On 24 March, NATO agreed to take control of the no-fly zone from the initial coalition, while command of targeting ground units remained with the coalition's forces. NATO began officially enforcing the UN resolution on 27 March 2011 with assistance from Qatar and the United Arab Emirates. By June, reports of divisions within the alliance surfaced as only eight of the 28 member nations were participating in combat operations, resulting in a confrontation between US Defense Secretary Robert Gates and countries such as Poland, Spain, the Netherlands, Turkey, and Germany to contribute more, the latter believing the organization has overstepped its mandate in the conflict. In his final policy speech in Brussels on 10 June, Gates further criticized allied countries in suggesting their actions could cause the demise of NATO. The German foreign ministry pointed to "a considerable [German] contribution to NATO and NATO-led operations" and to the fact that this engagement was highly valued by President Obama.

While the mission was extended into September, Norway that day announced it would begin scaling down contributions and complete withdrawal by 1 August. Earlier that week it was reported Danish air fighters were running out of bombs. The following week, the head of the Royal Navy said the country's operations in the conflict were not sustainable. By the end of the mission in October 2011, after the death of Colonel Gaddafi, NATO planes had flown about 9,500 strike sorties against pro-Gaddafi targets. A report from the organization Human Rights Watch in May 2012 identified at least 72 civilians killed in the campaign.
Following a coup d'état attempt in October 2013, Libyan Prime Minister Ali Zeidan requested technical advice and trainers from NATO to assist with ongoing security issues.

NATO has twenty-nine members, mainly in Europe and North America. Some of these countries also have territory on multiple continents, which can be covered only as far south as the Tropic of Cancer in the Atlantic Ocean, which defines NATO's "area of responsibility" under Article 6 of the North Atlantic Treaty. During the original treaty negotiations, the United States insisted that colonies such as the Belgian Congo be excluded from the treaty. French Algeria was however covered until their independence on 3 July 1962. Twelve of these twenty-nine are original members who joined in 1949, while the other seventeen joined in one of seven enlargement rounds.

From the mid-1960s to the mid-1990s, France pursued a military strategy of independence from NATO under a policy dubbed "Gaullo-Mitterrandism". Nicolas Sarkozy negotiated the return of France to the integrated military command and the Defence Planning Committee in 2009, the latter being disbanded the following year. France remains the only NATO member outside the Nuclear Planning Group and unlike the United States and the United Kingdom, will not commit its nuclear-armed submarines to the alliance. Few members spend more than two percent of their gross domestic product on defence, with the United States accounting for three quarters of NATO defense spending.

New membership in the alliance has been largely from Central and Eastern Europe, including former members of the Warsaw Pact. Accession to the alliance is governed with individual Membership Action Plans, and requires approval by each current member. NATO currently has two candidate countries that are in the process of joining the alliance: Bosnia and Herzegovina and the Republic of Macedonia.
In NATO official statements, the Republic of Macedonia is always referred to as the "former Yugoslav Republic of Macedonia", with a footnote stating that "Turkey recognizes the Republic of Macedonia under its constitutional name". Though Macedonia completed its requirements for membership at the same time as Croatia and Albania, who joined NATO in 2009, its accession was blocked by Greece pending a resolution of the Macedonia naming dispute. In order to support each other in the process, new and potential members in the region formed the Adriatic Charter in 2003. Georgia was also named as an aspiring member, and was promised "future membership" during the 2008 summit in Bucharest, though in 2014, US President Barack Obama said the country was not "currently on a path" to membership.

Russia continues to oppose further expansion, seeing it as inconsistent with informal understandings between Soviet leader Mikhail Gorbachev and European and American negotiators that allowed for a peaceful German reunification. NATO's expansion efforts are often seen by Moscow leaders as a continuation of a Cold War attempt to surround and isolate Russia, though they have also been criticised in the West. A June 2016 Levada poll found that 68% of Russians think that deploying NATO troops in the Baltic states and Poland – former Eastern bloc countries bordering Russia – is a threat to Russia. In contrast 65% of Poles surveyed in 2017 Pew Research Center report identified Russia as a "major threat", with an average of 31% saying so across all NATO countries, and 67% of Poles surveyed in 2018 favour US forces being based in Poland. Of non-CIS Eastern European countries surveyed by Gallup in 2016, all but Serbia and Montenegro were more likely than not to view NATO as a protective alliance rather than a threat.

Ukraine's relationship with NATO and Europe has been politically controversial, and improvement of these relations was one of the goals of the "Euromaidan" protests that saw the ousting of pro-Russian President Viktor Yanukovych in 2014. In March 2014, Prime Minister Arseniy Yatsenyuk reiterated the government's stance that Ukraine is not seeking NATO membership. Ukraine's president subsequently signed a bill dropping his nation's nonaligned status in order to pursue NATO membership, but signaled that it would hold a referendum before seeking to join. Ukraine is one of eight countries in Eastern Europe with an Individual Partnership Action Plan. IPAPs began in 2002, and are open to countries that have the political will and ability to deepen their relationship with NATO.

A 2006 study in the journal "Security Studies" argued that NATO enlargement contributed to democratic consolidation in Central and Eastern Europe.

The Partnership for Peace (PfP) programme was established in 1994 and is based on individual bilateral relations between each partner country and NATO: each country may choose the extent of its participation. Members include all current and former members of the Commonwealth of Independent States. The Euro-Atlantic Partnership Council (EAPC) was first established on 29 May 1997, and is a forum for regular coordination, consultation and dialogue between all fifty participants. The PfP programme is considered the operational wing of the Euro-Atlantic Partnership. Other third countries also have been contacted for participation in some activities of the PfP framework such as Afghanistan.

The European Union (EU) signed a comprehensive package of arrangements with NATO under the Berlin Plus agreement on 16 December 2002. With this agreement, the EU was given the possibility to use NATO assets in case it wanted to act independently in an international crisis, on the condition that NATO itself did not want to act – the so-called "right of first refusal". For example, Article 42(7) of the 1982 Treaty of Lisbon specifies that "If a Member State is the victim of armed aggression on its territory, the other Member States shall have towards it an obligation of aid and assistance by all the means in their power". The treaty applies globally to specified territories whereas NATO is restricted under its Article 6 to operations north of the Tropic of Cancer. It provides a "double framework" for the EU countries that are also linked with the PfP programme.

Additionally, NATO cooperates and discusses its activities with numerous other non-NATO members. The Mediterranean Dialogue was established in 1994 to coordinate in a similar way with Israel and countries in North Africa. The Istanbul Cooperation Initiative was announced in 2004 as a dialog forum for the Middle East along the same lines as the Mediterranean Dialogue. The four participants are also linked through the Gulf Cooperation Council.

Political dialogue with Japan began in 1990, and since then, the Alliance has gradually increased its contact with countries that do not form part of any of these cooperation initiatives. In 1998, NATO established a set of general guidelines that do not allow for a formal institutionalisation of relations, but reflect the Allies' desire to increase cooperation. Following extensive debate, the term "Contact Countries" was agreed by the Allies in 2000. By 2012, the Alliance had broadened this group, which meets to discuss issues such as counter-piracy and technology exchange, under the names "partners across the globe" or "global partners". Australia and New Zealand, both contact countries, are also members of the AUSCANNZUKUS strategic alliance, and similar regional or bilateral agreements between contact countries and NATO members also aid cooperation. Colombia is the NATO’s latest partner and Colombia has access to the full range of cooperative activities NATO offers to partners; Colombia became the first and only Latin American country to cooperate with NATO.

All agencies and organizations of NATO are integrated into either the civilian administrative or military executive roles. For the most part they perform roles and functions that directly or indirectly support the security role of the alliance as a whole.

The civilian structure includes:

The military structure includes:

The organizations and agencies of NATO include:

The NATO Parliamentary Assembly (NATO PA) is a body that sets broad strategic goals for NATO, which meets at two session per year. NATO PA interacts directly with the parliamentary structures of the national governments of the member states which appoint Permanent Members, or ambassadors to NATO. The NATO Parliamentary Assembly is made up of legislators from the member countries of the North Atlantic Alliance as well as thirteen associate members. It is however officially a different structure from NATO, and has as aim to join together deputies of NATO countries in order to discuss security policies on the NATO Council.Similar organizations: