<P> After 1945, the isolationist pattern characterizing the inter-war period had ended for good . It was Franklin Roosevelt policy to establish a new international organization that would be much more effective than the old League of Nations, and avoid its flaws . He successfully sponsored the formation of the United Nations . </P> <P> The United States was a major force in establishing the United Nations in 1945, hosting a meeting of fifty nations in San Francisco . Avoiding the rancorous debates of 1919, where there was no veto, the US and the Soviet Union, as well as Britain, France and China, became permanent members of the Security Council with veto power . The idea of the U.N. was to promote world peace through consensus among nations, with boycotts, sanctions and even military power exercised by the Security Council . It depended on member governments for funds and had difficulty funding its budget . In 2009, its $5 billion budget was funded using a complex formula based on GDP; the U.S. contributed 20% in 2009 . However, the United Nations' vision of peace soon became jeopardized as the international structure was rebalanced with the development and testing of nuclear weapons by major powers . </P> <P> From the late 1940s until 1991, world affairs were dominated by the Cold War, in which the U.S. and its allies faced the Soviet Union and its allies . There was no large - scale fighting but instead numerous regional wars as well as the ever - present threat of a catastrophic nuclear war . </P> <P> In 1948 the United States enacted the Marshall Plan, which supplied Western Europe--including Germany--with $13 billion USD in reconstruction aid . Staff on vetoed any participation by East European nations . A similar program was operated by the United States to restore the Japanese economy . The U.S. actively sought allies, which it subsidized with military and economic "foreign aid", as well as diplomatic support . Most nations aligned with either the Western or Eastern camp, but after 1960 the Soviets broke with China as the Communist movement worldwide became divided . Some countries, such as India and Yugoslavia, tried to be neutral . Rejecting the rollback of Communism by force because it risked nuclear war, Washington developed a new strategy called containment to oppose the spread of communism . The containment policy was developed by U.S. diplomat George Kennan in 1947 . Kennan characterized the Soviet Union as an aggressive, anti-Western power that necessitated containment, a characterization which would shape US foreign policy for decades to come . The idea of containment was to match Soviet aggression with force wherever it occurred while not using nuclear weapons . The policy of containment created a bipolar, zero - sum world where the ideological conflicts between the Soviet Union and the United States dominated geopolitics . Due to the antagonism on both sides and each countries' search for security, a tense worldwide contest developed between the two states as the two nations' governments vied for global supremacy militarily, culturally, and influentially . </P>

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