Article II, Section 2 of the U.S. Constitution grants the President the power to negotiate alliances with the “Advice and Consent of the Senate.” 

Presidents made limited use of that power in the first century and a half of American history, following the precedent set by the first President. In his Farewell Address, George Washington declared: “It is our true policy to steer clear of permanent alliances with any portion of the foreign world.” Washington believed that the most sensible course for the young Republic to preserve its own independence and freedom was to stay out of any alliances, and especially to steer clear of any connection to the ongoing geopolitical contest among the great powers of Europe. Following Washington’s example, his successors relied on trade agreements and isolationist proclamations such as the Monroe Doctrine and Roosevelt Corollary to keep American forces on this side of the Atlantic, and Europeans out.

Even participation in the First World War could not overcome this ingrained reluctance to make permanent alliances. President Woodrow Wilson tried to link the United States to its European partners in the League of Nations, but failed to convince the Senate to endorse the plan in the Treaty of Versailles.

That all changed in April 1949, when the U.S. joined ten European partners and Canada in creating the most important treaty of our time: the North Atlantic Treaty Organization (NATO).

To understand NATO’s place in American history and current geopolitics requires a look back, and a look forward.

As the World War II partnership with the Soviet Union gave way to the bi-polar global confrontation known as the Cold War, the United States, which had already begun providing economic assistance to Europe with the Marshall Plan, encouraged Europeans to provide for their common defense against the Soviet threat. In 1948, Great Britain and France joined Belgium, the Netherlands, and Luxembourg to form the Brussels Pact, pledging to defend one another should they be attacked.

Even as they signed that agreement, however, European leaders such as British Foreign Minister Ernest Bevin also sought a clear security guarantee from the United States. President Harry Truman and Secretary of State Dean Acheson agreed that such a guarantee would serve both American and European interests in maintaining the stability and security of the West. A year of negotiations and increasing tensions with the Soviets led in April 1949 to the NATO Treaty, which included the original members of the Brussels Pact, along with Canada, Portugal, Iceland, Italy, Denmark, and Norway.

Linking North America and Europe against any possible Soviet threats, NATO became the centerpiece of transatlantic cooperation during the Cold War.

The keystone of the NATO treaty is Article V, in which the treaty members agreed “that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all.”

NATO was initially just an American promise to come to the defense of Western Europe after a Soviet attack. Over time, however, NATO developed formal permanent structures, introducing an integrated military command with permanently stationed troops along the Iron Curtain, and affirming its political role as a forum for coordinating work on arms control and the reduction of international tensions.

As a result, NATO today has a two-headed structure. The military side is led by the Supreme Allied Commander (an American General or Admiral), with subordinate commanders for each region. The political organization became the NATO Council and NATO Parliamentary Assembly and is represented by a Secretary General (a European diplomat). Though originally housed in Paris, NATO headquarters has been outside of Brussels since 1966, and recently moved into a newly constructed complex.

NATO also gradually added more members to its original twelve, including Greece and Turkey in 1952, West Germany in 1955, and Spain in 1982. After the end of the Cold War and the dissolution of the Soviet-led Warsaw Pact, some analysts suggested NATO should simply disband as well, since its mission of defending Western Europe from Soviet invasion had become moot. Over the course of the 1990s, however, American and European leaders agreed NATO could still play an important role in maintaining European-American ties as well as encouraging democratic development and security—not just in Europe, but around the world. Thus, the alliance continued to expand to twenty-nine members, adding thirteen Central and Eastern European former members of the Communist bloc, and has also extended its activities to include operations in locations as diverse as the former Yugoslavia and Afghanistan, as well as anti-piracy operations in the Indian Ocean.

NATO expansion has not been without controversy. While adding Central and Eastern European states has encouraged democracy and regional cooperation, it has also alienated Russia, whose relationship with NATO remains complicated by historical resentments and contemporary disagreements. Russia even intervened in Georgia and Ukraine to discourage them from joining the Alliance. Debates about overseas deployments and relative levels of defense spending—an issue NATO hands refer to as “burden sharing”—have also raised the question of whether a military alliance conceived in the Cold War has a future at all.

The discussion about NATO’s future has become especially controversial lately, and this is not necessarily a bad thing. Any alliance of sovereign and independent democracies must be open to debate and be able to adapt to changing circumstances. By helping to preserve the security and freedom of its members for nearly seventy years, NATO has provided a framework within which the democracies of the West could carry on that debate. Whatever shape it takes in the future, NATO has served its purpose very well and remains one of the greatest accomplishments of modern American foreign policy.