World War II brought American isolationism to an end. The first steps moving the United States away from neutrality took the form of executive agreements (such as the destroyers-for-bases accord of 3 September 1940) permitting increased aid to England. But it was the crucially important Lend-Lease Act (11 March 1941) that, even prior to Pearl Harbor, introduced the United States into the front stage of world diplomacy and at the same time gave the latter an entirely new form. Franklin Roosevelt's bold initiatives, combined with the enormous growth of American economic power, yielded a new and unprecedented diplomatic form, that of foreign aid. While traditional diplomacy had been conducted between great and small powers, and Wilsonian diplomacy had established the principle of equality, diplomacy after lend-lease assumed a dual nature. On the one hand, relations between nations deemed to be equals continued to be conducted by ambassadors. On the other hand, there emerged a new form of relationship between two countries, whereby one became the aid donor and the other the aid recipient. Assistance, which could be economic, military, or technical, was administered by government officials who were not ambassadors and generally were dependent on them only nominally. Aid accords tended to evolve in the following manner: first, voting of a general law by Congress; second, voting of appropriations; third, aid accords concluded with the beneficiaries.
Many programs, each involving a set of accords, were elaborated in this fashion: lend-lease (11 March 1941–21 August 1945); bilateral aid accords (1945–1948); the Marshall Plan (5 June 1947), leading to the European Recovery Program (April 1948); Point Four (aid to under-developed countries, 20 January 1949); and the Mutual Security Program (replacing the European Recovery Program). These programs led to the signing of hundreds of accords, some of which were treaties. Occasionally, an accord has been considered an agreement by the United States and a treaty by the other party. This was the case, for example, with the Franco-American Mutual Aid Accord of 27 January 1950.
President Franklin D. Roosevelt took considerable precautions so that the Senate would not refuse American participation in the new international organization whose principles he had outlined as early as 1941 in the Atlantic Charter. The conferences at Tehran (28 November–1 December 1943), Dumbarton Oaks (August–October 1944), and Yalta (4–11 February 1945) had elaborated the underlying principles of the United Nations. Roosevelt constantly consulted with the Senate, endeavoring to make his collective security policy a bipartisan affair. The founding conference of the United Nations was held in San Francisco from 25 April to 26 June 1945. Forty-six nations signed the charter, which the United States was the first to adopt, the Senate approving it on 29 July 1945 with near unanimity.
It should be noted that the right of veto held by the five permanent members of the Security Council protected the United States, in the last resort, against any obligations imposed by the council. At the same time, the locating of the UN headquarters in the United States (Lake Success Accord of 26 June 1947, between the United Nations and the United States) contributed to the popularity of the organization in America. Thereafter, actively involved in the life of the international organization, the United States found that it had adopted Wilsonian "internationalism," which constituted a break with tradition.
The main preoccupation of American treaties following World War II was security cooperation in a postwar climate characterized by ideological conflict with the Soviet Union, bipolarization of the world between these two powers, destruction of the colonial empires and the emergence of nearly ninety new nations, economic inequality, and reliance on atomic weapons as a deterrent. The United States, therefore, could no longer pursue its traditional (moderate and reserved) policy of treaty making. Indeed, since 1945 it has concluded more treaties (not counting agreements) than any other nation, and almost all have been of a new type. They have included aid accords, participation in the United Nations, peace treaties, treaties of alliance, treaties linked to deterrence, and treaties dealing with a far wider range of issues than had traditionally been the case: human rights, ecology, the environment and resources, global warming, the outlawing of chemical and other weapons of mass destruction, access to and the future use of outer space, copyright and the protection of intellectual property, and biotechnology and human cloning.
The existence of fundamental disagreements between the Soviet Union and the United States prevented the conclusion of a peace treaty with Germany. The creation of the Federal Republic of Germany in September 1949 was facilitated by the fact that the three Western occupying powers had unified their zones economically and had made procedural provisions for the reconstitution of a German nation (the London convention regarding Germany, June 1948). Having also defined the respective areas of responsibility for the future state and the occupiers (the Washington accords regarding Germany, April 1949), they began transferring an increasingly important role to the former. Finally, a simple peace protocol, the Treaty of Paris (October 1954), ended the occupation, replacing it with the presence of "security forces." The treaty was approved by the Senate on 1 April 1955.
For similar reasons it proved impossible to sign a common peace treaty including both Japan and the Soviet Union, despite the efforts of John Foster Dulles in 1947. Although formal surrender ceremonies had been held aboard the USS Missouri on 2 September 1945, it was not until 8 September 1951 that the United States and forty-eight other countries concluded a peace settlement with Japan, the San Francisco Peace Treaty. The Soviet Union, although it attended the San Francisco meeting, abstained. The Senate gave its consent with reservations on 20 March 1952 by a vote of 66 to 10.
In the case of Austria, which the victors intended to keep permanently separate from Germany, it required ten years of negotiations before the Soviet Union decided, in exchange for a guarantee of the country's neutrality, to join the other occupying powers in signing the Austrian State Treaty. Following Senate approval, President Dwight D. Eisenhower ratified it on 24 June 1955.
All of the above was accomplished outside the procedural framework provided for by the Potsdam Conference of 1945. On that occasion, a council of foreign ministers (of the United States, the Soviet Union, the United Kingdom, France, and China) was created for the purpose of negotiating the various peace treaties, on the understanding that of the five countries, only those that had signed armistice agreements with the defeated nations would participate in treaty negotiations (France being considered as having signed an armistice with Italy). In principle, this should have excluded the United States from the peace treaty with Finland. In fact, however, all the treaties with the "Axis satellites" were discussed by the Big Four (China being absent). Many meetings of the council took place in 1945 and 1946. They produced five peace treaties, signed by the American secretary of state in Washington and by the other countries (Italy, Finland, Romania, Bulgaria, and Hungary) on 10 February 1947 in Paris. The Senate approved them on 4 June 1947.
Two further meetings of the council took place, in Moscow (10 March–24 April 1947) and London (25 November–December 1947). These negotiations were brought to a halt by U.S. adoption of containment policy (the Truman Doctrine of 12 March 1947 and the Marshall Plan of 5 June 1947), the creation of the Kominform by the Soviet Union, and the increasing tensions of the Cold War in 1948 (the Berlin Blockade). While such diplomacy did revive sporadically, beginning with the Paris conference of 23 May–20 June 1949, which ended the Berlin Blockade, and including several summit meetings, it did not bring about any peace treaties.
Nor were peace treaties enacted—only armistice agreements—after the Korean War (27 July 1953), after French withdrawal from Indochina (the Geneva Accords of 20 July 1954 were rejected by the United States), or after the war in Vietnam. In the latter case, after five years of negotiations involving the United States, North Vietnam, South Vietnam, and the National Liberation Front, an accord was finally reached on 28 January 1973. Although it had the breadth and scope of a peace treaty, it was simply an executive agreement that, on the American side, went into effect with its signing by Secretary of State Henry Kissinger, and not after approval by the Senate.
As soon as World War II ended, American officials sought to give new form to Pan-Americanism. They began with a provisional alliance, excluding Argentina, that was signed at Chapultepec, Mexico, in March 1945. The signatories undertook to consult with one another in the event of aggression or the threat of aggression. At the inter-American conference "for the maintenance of continental peace and security" at Rio de Janeiro (15 August–2 September 1947), the twenty-one republics (except Nicaragua, which was absent) signed a reciprocal inter-American assistance treaty, which contained essentially the same provisions as the Pact of Chapultepec. Sanctions could be voted collectively against aggressors. Finally, on 30 April 1948, the Charter of the Organization of American States was signed, making the Pan American Union a regional organization within the framework of the United Nations. The United States did not ratify the charter until June 1951. Despite their innovative elements, these alliances invariably fell within the traditional perspective of the Monroe Doctrine. The same was not the case with later alliances.
The Atlantic Pact of 4 April 1949, which created NATO, was a reaction to the Cold War. The five European signatories of the treaty of alliance of Brussels (17 March 1948) gave the premier of France (Georges Bidault) and the foreign minister of England (Ernest Bevin) the task of requesting the American secretary of state, George C. Marshall, to secure his country's participation. The necessity of defending western Europe seemed so critical that on 11 June 1948 the Senate adopted, by a vote of 64 to 4, the Vandenberg Resolution, authorizing the president to conclude peacetime alliances outside the Western Hemisphere. This represented a break with prior American foreign policy, which had avoided alliances since the end of the eighteenth century. Negotiations were prolonged, since it was necessary to await the outcome of the presidential elections, in which Harry S. Truman was the victor.
A preliminary draft of 28 December was followed on 15 March 1949 by the version ultimately signed by the five (France, the United Kingdom, Belgium, the Netherlands, and Luxembourg), the United States, and Canada. They then invited Norway, Denmark, Iceland, Portugal, and Italy to participate. The treaty, published on 18 March, before it had been signed, provided for consultation in the event of threatened or actual aggression and for military assistance, which was not to be absolutely automatic. (In the event of aggression in the North Atlantic region, each party would undertake "immediately, individually and in accord with the other parties, whatever action it shall judge necessary, including the use of armed force.") The signing by the twelve members took place in Washington, D.C., on 4 April 1949. The following day, the U.S. government granted a request for military aid, which was voted by the Congress on 14 October, a few days after the first Soviet atomic explosion.
The treaty was supplemented by the creation of the North Atlantic Council (18 May 1950) and of an integrated command in Europe known as Supreme Headquarters Allied Powers in Europe (SHAPE, 19 December 1950). Greece and Turkey joined the alliance in February 1952 and the Federal Republic of Germany in May 1955. On 13 September 2001, two days into the crisis created by the horrific suicide attacks by Islamic terrorists on the World Trade Center towers in New York City and the Pentagon outside Washington, D.C., NATO Secretary General Lord Robertson (of Scotland) announced in Brussels that NATO (numbering nineteen members by 2001) stood ready to back U.S. military retaliation to the terror attack described by President George W. Bush as "an act of war." For the first time in its fifty-two-year history, NATO was invoking Article 5 of the alliance's charter, which states that "an armed attack against one or more of the nations in Europe or North America shall be considered an attack against them all," and if such an armed attack occurs, each of them will take the necessary action to assist the party so attacked, "including the use of armed force.
At the same time as the Japanese peace treaty, the United States concluded three new alliances: the Pacific Security Pact with Australia and New Zealand (ANZUS) on 1 September 1951, an alliance with the Philippines on 30 August 1951, and a security treaty with Japan on 8 September 1951. Provisions of ANZUS were invoked for the first time in September 2001, by Australian Prime Minister John Howard, in response to the attack on the World Trade Center and the Pentagon. Later, the United States joined the Southeast Asia Treaty Organization (SEATO), created by the Treaty of Manila of 8 September 1954. The other signatories of this collective defense treaty for Southeast Asia were the United Kingdom, France, Australia, New Zealand, the Philippines, Thailand, and Pakistan. Article 4 guaranteed the political independence and territorial integrity of South Vietnam, Laos, and Cambodia, although there was no formal alliance with these three states.
The United States also concluded bilateral mutual defense treaties with South Korea (1 October 1953), Pakistan (19 May 1954), and the Republic of China, or Taiwan (2 December 1954). This last treaty gave rise to a curious situation. Anxious to dramatize the danger presented by the People's Republic of China to Taiwan and its dependencies, the administration, without waiting for Senate approval (ultimately obtained in February 1955), had the two houses of Congress vote a joint resolution on 25 and 28 January, respectively (the votes were 409 to 3 in the House of Representatives and 95 to 3 in the Senate), authorizing the president to protect Taiwan against attack.
Thus, the United States, hostile to all military alliances for a century and a half, had enmeshed itself in the most extensive system of alliances in the history of the world, incorporating, at its peak, forty-four allies: twenty American republics, Canada, Australia, New Zealand, thirteen European nations in NATO, Japan, and seven Asian nations (including Iraq).