As World War II ended and the relationship between the Soviet Union and other Allied powers deteriorated, the United States, Canada, and a group of ten European countries organized themselves for a new geopolitical reality. In 1949, they created the North Atlantic Treaty Organization (NATO), an alliance with the aim of preserving a free, integrated, and democratic Europe, particularly against the Soviet Union.

In international relations, an alliance is a group of countries that come together to promote their common security interests. In many cases, alliances promise military support if one member is threatened, a formal commitment known as mutual security. The core of NATO’s strength comes from Article 5 of its founding treaty—a commitment that an attack on one member country will be considered an attack on the entire alliance. 

All kinds of countries benefit from alliances. For smaller, weaker countries that lack resources to mount a proper defense, joining an alliance can be the only realistic path to maintaining security and deterring potential foes. Larger or stronger countries use alliances to increase their military might and, sometimes, their influence over smaller countries, while also discouraging nuclear proliferation among smaller countries.

For over seven decades, NATO has endured, even as the common foe that it was organized against—the Soviet Union—disappeared. It successfully protected its members against Soviet aggression; no NATO member was ever attacked by the Soviet Union. Today, the alliance consists of thirty member countries and is an essential reason that Europe has remained mostly conflict-free since the end of World War II. But it has also recently taken on faraway missions in places like the Middle East to prevent humanitarian suffering, with mixed results, and come under increased scrutiny due to many of its European members not spending enough on their defense. These challenges come as many NATO countries consider Russia a renewed threat to Europe’s security.

This timeline explores NATO’s history—from its origins as a bulwark against the Soviet Union to its present-day operations far from Europe’s shores—and examines the effects of its expanding membership, evolving mission, and recent funding concerns, all of which point toward an uncertain future.

NATO Origins

As World War II came to a close, the alliance between the Soviet Union and Western powers deteriorated. Europe needed a plan for maintaining long-term peace. Under terms outlined at the Yalta and Potsdam Conferences, Soviet Premier Joseph Stalin was given temporary control of Poland and a portion of Germany. However, it quickly became clear that the Soviet Union had greater ambitions, as it sponsored communist-led coups in Czechoslovakia and surrounding east European territories. Fearful of further Soviet encroachment on Western Europe, these countries discussed forming an organization capable of providing mutual security.

The opening speech at the NATO Summit talks in Paris on December 14, 1957.

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British Foreign Secretary Ernest Bevin signs the North Atlantic Treaty in Washington while Sir Oliver Franks, the British ambassador to the United States, watches on April 4, 1949.

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The Birth of NATO

The Soviet Union’s alarming expansion and failure to comply with the terms of the Potsdam and Yalta Conferences led to the creation of NATO as a means to preserve a unified, democratic Europe. The defensive alliance was formed in 1949 and consisted of twelve members: the United States, Canada, and ten European countries. NATO’s founding members structured the organization so that all decisions would be made through consensus. Despite the alliance’s egalitarian structure, the United States’ leading role was clear from the start; a supreme allied commander Europe (SACEUR), a position that an American has always held, leads NATO’s military operations.

Foreign ministers from NATO counties look on as Pierre Mendes-France, the French foreign minister, signs the treaties making West Germany a part of NATO on October 22, 1954.

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Early Expansion to Bring in West Germany

NATO’s founding members believed that expanding the alliance was crucial to ensuring peace in Europe. They offered membership to Greece and Turkey in 1952 and West Germany in 1955, the latter an especially consequential decision given Germany’s history of provoking conflict in Europe. With its entry into NATO, West Germany became more integrated with Western Europe and committed to never manufacturing weapons of mass destruction. In the words of NATO’s first secretary-general, the purpose of NATO was to “keep the Soviet Union out, the Americans in, and the Germans down.”

The Soviet delegation present for the signing of the Warsaw Pact on May 14, 1955.

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Soviet Union and the Warsaw Pact

West Germany’s entrance into NATO prompted the Soviet Union to create its own alliance: the Warsaw Pact. Although the Soviet Union already had bilateral defense agreements with most of its communist neighbors, the Warsaw Pact formalized these relations into a bloc that could act in a unified manner. By focusing on integrating the militaries of Warsaw Pact countries, the Soviet Union could control smaller east European countries more effectively, shielding them from NATO influence. The Soviet Union went to great lengths to retain these allies: when Hungarians demonstrated in 1956, calling for greater political and economic freedoms and the country’s withdrawal from the Warsaw Pact, the Soviet Union sent in tanks and crushed the protests, killing 2,500 Hungarians.

U.S. President Ronald Reagan signs the INF Treaty in the East Room of the White House on December 8, 1987.

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Dual-Track Decision a Risky Success

During the Cold War, NATO deployed hundreds of U.S. missiles close to the borders of several Warsaw Pact countries, including the Soviet Union. At the same time, NATO leveraged the presence of these warheads to negotiate a dismantling of all short- and intermediate-range missiles with the Soviet Union. Ultimately, the strategy (known as the dual-track decision) was successful: the two sides reached an arms control agreement in 1987. The NATO-sponsored military buildup was risky and controversial among the European public, as it would have made any conflict that did erupt much deadlier.

A big section of the Berlin Wall is lifted by a crane as East Germany starts to dismantle the wall near the Brandenburg Gate in East Berlin on February 20, 1990.


Dissolution of the Soviet Union

In 1991, prompted by domestic political reforms and democratic momentum in the countries within its orbit, the Soviet Union disintegrated into Russia and fourteen other countries. This collapse and the dissolution of the Soviet-led Warsaw Pact marked a swift end to the Cold War. NATO had successfully achieved its mission of deterring armed conflict on the continent, keeping the Cold War mostly cold. It is rare for an alliance born in one strategic context to endure once that strategic context fundamentally changes. With the fall of the Soviet Union and the disappearance of its common foe, would NATO dissolve or persevere and take on new missions?

As Cold War Ends, NATO Faces Inflection Point

At the end of the Cold War, NATO faced the question of whether it should continue to exist. Rather than retire one of history’s most successful military partnerships, NATO officials decided to reimagine the group’s mission. But many questions remained: Would the alliance stay the same size or admit new members? Would it remain a purely defensive alliance or expand its mission? Over the next decade, NATO expanded its membership and confronted new forms of instability outside its members’ borders.

Heads of state and NATO Secretary General Manfred Woerner (center) pose for photographers at the NATO summit in Brussels on January 10, 1994.

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U.S. President Bill Clinton wipes away tears of laughter as he leans on Russian President Boris Yeltsin after a remark by Yeltsin during a joint press conference following their talks in Hyde Park, New York, on October 23, 1995.

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Partnership for Peace With Russia

The first step in reimagining a post–Cold War NATO was an initiative called Partnership for Peace. Its main objectives were forming relationships with former Soviet countries and demonstrating that NATO did not intend to disappear after the Cold War. Although participation in the partnership did not guarantee former Warsaw Pact countries entry into NATO, it was widely seen as a first step toward obtaining membership. Thirteen east European countries—including Russia—worked with NATO allies and cooperated on multilateral activities like humanitarian assistance, peacekeeping, and crisis management. Critics of NATO’s activities in the immediate post-Cold War period believe the alliance should have done more to integrate Russia and provide the country with greater economic assistance, arguing this could have prevented Russian alienation.

Two F-16 Fighting Falcon planes of the U.S. Air Force take off for Bosnia from the Aviano Nato Air Base in November 1994.

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NATO Involvement in Serbia

In 1995, Bosnian Serbs violated a UN Security Council resolution during the Bosnian War. In response, NATO launched an air campaign against the Bosnian army. In 1999, violence resurged in the region as Serbian authorities persecuted a group of ethnic Albanians who were calling for an independent country. NATO concluded that attacking Serbia was justified in order to prevent mass atrocities. Led by the United States, the alliance launched another extensive bombing campaign. This marked the start of NATO’s transformation from a purely defensive alliance into a large, coordinated, and powerful military force operating beyond its members’ borders.

Polish President Aleksander Kwasniewski (right) makes a point during his speech at the 14th international NATO Workshop on Political-Military Decision Making at Prague Castle on June 22, 1997, while General George Joulwan, the supreme commander of allied forces in Europe, listens.

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Challenges of NATO Enlargement

NATO continued its expansion in 1999, adding the Czech Republic, Hungary, and Poland. The alliance grew again in 2004, extending membership to seven east European countries, many of which were former Soviet republics. The United States largely drove this period of growth, believing that expanding NATO would deter future Russian aggression and provide members with the security they needed to allow for the transition to democracy. However, the expansion was not without consequences. Russia perceived NATO’s creep into Eastern Europe as a direct threat to its security and influence across the region and was alienated by the expansion. And as NATO grew, member countries worried that the additional obligations would stretch the alliance thin.

9/11 Ushers in New Chapter

The September 11, 2001 attacks had a major effect on NATO. Not only did they result in the first—and only—time the alliance invoked Article 5, they also demonstrated the increasing interconnectedness of the world. NATO used this reality as justification to fight threats at their source, even if those were far away from NATO homelands. In the opening years of the new century, NATO adopted a more expansive definition of what it meant to protect its members’ national interests and transformed from a traditional defensive alliance into a collective of like-minded countries willing to pursue broader objectives.

A German crew member of a NATO Airborne Warning and Control Systems (AWACS) aircraft inspects the E-3A Aircraft prior to its departure at the NATO air base in Geilenkirchen, Germany, on October 10, 2001.

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An Afghan army truck (right) drives beside a NATO-led International Security Assistance Force vehicle outside of Kabul on December 17, 2004.

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9/11 Response

On September 11, 2001, militants from the terrorist group al-Qaeda hijacked four planes and used them as weapons to kill 2,977 people in the United States. The 9/11 attacks prompted the first—and only—invocation of Article 5, under which NATO considered the attacks to be against all of its members. In response, NATO spearheaded an anti-Taliban coalition in Afghanistan, which constituted its first mission outside the North Atlantic. Since then, the mission has continuously evolved, and, nearly two decades later, NATO forces are still in Afghanistan.

An F-16 takes off from Leeuwarden Airbase for the Italian island of Sardinia on March 24, 2011.

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Questions on Expanded Mission After Chaos in Libya

In 2011, the UN Security Council permitted NATO to enforce a no-fly zone over Libya after the country’s dictator, Muammar al-Qaddafi, threatened the country’s civilians. But NATO’s mission quickly expanded from simply grounding Qaddafi’s air force into a broader political mission to remove Qaddafi from power. In the following months, NATO-backed rebels took over most of Libya and executed Qaddafi. Although NATO leaders hoped Qaddafi’s ouster would mark the end of Libya’s violence, the country soon spiraled into even greater chaos. The unintended consequences of the Libya campaign raised questions about the effectiveness of NATO’s expanding mission.

Ukrainian Foreign Minister Andriy Deshchytsia (left) waits for the start of a NATO-Ukraine foreign ministers meeting at the NATO headquarters in Brussels on April 1, 2014.

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Renewed Relevance in Face of Russian Aggression

In 2014, Russia invaded Ukraine and annexed Crimea—a reminder to NATO countries that Russia still threatened democracy in Europe. NATO responded by suspending all military and civilian cooperation with Russia and promising to send more troops to its members in Eastern Europe. The continued need for an alliance to defend Europe’s democracies is particularly acute in the Baltic countries Estonia, Latvia, and Lithuania, which are seen as especially vulnerable to Russian military force.

An Uncertain Future

What does the future hold for NATO? Although the alliance was united during the Cold War in its objective to contain the Soviet Union, members today don’t always view their national interests as compatible with those of their allies. (This precariousness was on full display in late 2019 when the United States and Turkey, two NATO members, stood on opposing sides of the Syrian civil war and nearly attacked each other.) Although the alliance remains broadly popular among the public in its member countries, some NATO leaders have been explicit about troubles on the horizon: French President Emmanuel Macron warned in 2019 that divisions within NATO’s ranks risked making the alliance “brain-dead.” And U.S. President Donald J. Trump has repeatedly threatened to withdraw the United States from NATO unless European countries pledge to increase their defense spending. Far from being resolved, these tensions point to an uncertain future for NATO in a Europe that is still not fully free from threats.

U.S. Secretary of Defense Mark Esper (left) and NATO Secretary General Jens Stoltenberg participate in a joint press conference at the NATO headquarters in Brussels on June 26, 2020.

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