After the close of World War II, a new and very different conflict rose to the forefront of American national attention: the Cold War. The Cold War pitted the communist Soviet Union against the capitalist U.S. and its Western Allies. While there was little actual violence, both sides considered the conflict to be severe and threatening. President Harry S. Truman, who had succeeded Franklin Roosevelt as president after the latter’s death in April 1945, found himself in an increasingly difficult and complex battle against communism. Dwight D. Eisenhower, who succeeded Truman as president in 1952, inherited the conflict.

After Germany’s defeat in World War II, the leaders of the Allied countries met at a series of conferences to reshape the postwar world. Crucial among these was the Potsdam Conference in 1945, at which the Allies divided Germany into four zones, controlled by France, Britain, the U.S., and the USSR. Berlin, deep in the Soviet zone, was also divided among the four countries. During Potsdam, Truman informed Joseph Stalin that U.S. scientists had successfully detonated an atomic bomb, sparking a highly competitive nuclear arms race between the two countries.

In the late 1940s, the U.S. and USSR emerged as supreme among the nations of the world. The former wartime allies soon became bitter enemies. Both superpowers rushed to establish spheres of influence in Europe. Stalin wished to establish a buffer region of pro-Soviet states in Eastern Europe in order to prevent the recurrence of invasions such as those undertaken by Germany during the war. The Red Army established puppet governments in Bulgaria, Hungary, and Romania, adding to the ranks of independently established pro-Soviet governments in Albania and Yugoslavia. In 1945, Stalin disregarded the Yalta Declaration of Liberated Europe and disallowed free elections in Poland, which had served as a gateway to the Soviet Union for German invaders. In early March 1946, the former British prime minister Winston Churchill gave a speech at Westminster College in Missouri, coining the phrase the “iron curtain” to describe the USSR’s division of Eastern Europe from the West.

A combination of political, economic, and moral considerations led the U.S. government to oppose Soviet dominance of Eastern Europe. President Truman took a strong stance against the Soviet territorial advances, advocating a policy of containment. Under this policy, the U.S. would not attempt to change the post–World War II situation in Europe, but it would work to prevent further Soviet expansion through peaceful or military means.

Nuclear weapons played a central role in the possibility of military engagement between the U.S. and the USSR. In 1946, Truman proposed a plan to the United Nations to require the USSR to cease construction on any atomic weaponry, saying that only then would the U.S. destroy its growing arsenal. The Soviets rejected this plan and both sides rushed to develop weapons of mass destruction. In 1946, the federal government established the Atomic Energy Commission to oversee the development of nuclear energy and arms. The battle for nuclear dominance was characteristic of the Cold War, in which few battles were ever waged face to face.

In September 1949, the USSR detonated its first atomic bomb. This development, combined with the establishment of a communist regime in China, inspired a new and fiercer anticommunism in the U.S. government, expressed in its decision to more than triple the defense budget and to mount a furious campaign to develop a hydrogen bomb. The drive for the hydrogen bomb succeeded in the November 1952 detonation of an H-bomb in the Marshall Islands. But the American advantage was short-lived. In July 1953, the Russians detonated their own H-bomb.

Early in 1947, allies in a fragile Western Europe asked the U.S. to help fund the effort to prevent the rise of communist governments in Greece and Turkey. The economies and governments of Western Europe were nearing collapse. In March 1947, Truman asked a joint session of Congress to authorize military assistance to Turkey and Greece, depicting the issue as one of liberty versus oppression, and proclaimed that the U.S. would support people anywhere in the world facing “attempted subjugation by armed minorities or by outside pressures.” This proclamation, known as the Truman Doctrine, committed the U.S. to the role of global policeman.

The economic counterpart to the Truman Doctrine was the Marshall Plan, under which the U.S. pledged a great deal of financial assistance to Europe, specifically to stimulate European postwar recovery and to provide relief for the hungry, homeless, and desperate. Truman and his secretary of state George C. Marshall hoped the plan would eliminate economic and political instability, and strengthen European states against possible communist influence. As expected, the USSR rejected aid because of the Marshall Plan’s accompanying conditions of U.S. influence and control. By 1952, Congress had provided some $17 billion in aid, and the Western European economy had largely recovered.

France, Britain, and the United States gradually united their three zones of occupation within Germany and in 1948 announced their intention to create a West German Republic. In opposition to the proposed republic—which would have included West Berlin, situated deep in the Soviet zone—Stalin established the Berlin Blockade in June 1948, cutting off all rail and highway access to Berlin from the west. Choosing not to abandon Berlin or use military force, Truman ordered an airlift, called “Operation Vittles,” to supply West Berlin. The airlift continued until May 1949, when the USSR lifted the blockade. Western forces immediately pulled out of Germany and approved the creation of the Federal Republic of Germany, or West Germany. The USSR responded by creating the German Democratic Republic, or East Germany.

The heightened fear of conflict produced by the Berlin Blockade helped convince Western Europe of the need for a security alliance. In April 1949, ten Western European nations, Canada, and the U.S. established the North Atlantic Treaty Organization (NATO), and declared that an attack against any member of the alliance would be seen as an attack against all—a policy known as collective security. In July, the U.S. officially joined NATO, and Congress authorized $1.3 billion for military aid to NATO countries. The USSR responded by establishing a rival alliance, the Warsaw Pact, in 1955.