The Cold War took shape over the next five years, as both sides hardened their positions. After Japan’s surrender in September 1945, Truman cut off aid to the ailing U.S.S.R. In October he declared that the United States would never recognize any government established by force against the will of its people. In March 1946, former British prime minister Churchill informed an American audience that an “iron curtain” had fallen across the continent, dividing Europe into two antagonistic camps (Map 28.2).

The Soviet Union was indeed consolidating its hold on central and eastern Europe, using political repression to establish Soviet-style, one-party Communist dictatorships. At the same time, bitter civil wars in Greece and China pitted Communist revolutionaries against authoritarian leaders backed by the United States.

By early 1947, it appeared to many Americans that the U.S.S.R. was determined to export communism by subversion throughout Europe and around the world. The United States responded with the Truman Doctrine, aimed at “containing” communism to areas already under Communist governments. The United States, President Truman promised, would use diplomatic, economic, and even military means to resist the expansion of communism anywhere on the globe. In the first examples of containment policies in action, Truman asked Congress to provide military aid to anticommunist forces in the Greek Civil War (1944–1949) and counter the threat of Soviet expansion in Turkey. With American support, both countries remained in the Western bloc. The American determination to enforce containment hardened when the Soviets exploded their own atomic bomb in 1949. By the early 1950s, the U.S. government was restructuring its military to meet the Soviet threat, pouring money into defense spending, and testing nuclear weapons that dwarfed the destructive power of atomic bombs.

Military aid and a defense buildup were only one aspect of Truman’s policy of containment. In 1947, western Europe was still on the verge of economic collapse. Recognizing that an economically and politically stable western Europe would be an effective block against the popular appeal of communism, U.S. secretary of state George C. Marshall offered Europe economic aid — the Marshall Plan — to help it rebuild.

The Marshall Plan was one of the most successful foreign aid programs in history. When it ended in 1951, the United States had given about $13 billion in aid (equivalent to over $200 billion in 2014 dollars) to fifteen western European nations, and Europe’s economy was on the way to recovery. Marshall Plan funding was initially offered to East Bloc countries as well, but fearing Western interference in the Soviet sphere, they rejected the offer. In 1949, the Soviets established the Council for Mutual Economic Assistance (COMECON), an economic organization of Communist states intended to rebuild the East Bloc independently of the West. Thus the generous aid of the Marshall Plan was limited to countries in the Western bloc, which further increased Cold War divisions.

In the late 1940s, Berlin, the capital city of Germany, was on the frontline of the Cold War. Like the rest of Germany and Austria, Berlin had been divided into four zones of occupation. In June 1948, the Western allies replaced the currency in the western zones of Germany and Berlin, an early move in plans to establish a separate West German state sympathetic to U.S. interests. The currency reform violated the peace settlement and raised Stalin’s fears of the American presence in Europe. In addition, growing ties among Britain, France, Belgium, and the Netherlands convinced Stalin that a Western bloc was forming against the Soviet Union. In response, Stalin blocked all traffic through the Soviet zone of Germany to Berlin in an attempt to win concessions and perhaps reunify the city under Soviet control. Acting firmly, the Western allies coordinated around-the-clock flights of hundreds of planes over the Soviet roadblocks, supplying provisions to West Berliners and thwarting Soviet efforts to swallow up the western half of the city. After 324 days, the Berlin airlift succeeded, and the Soviets reopened the roads.

Success in breaking the Berlin blockade had several lasting results. First, it paved the way for the creation of two separate German states in 1949: the Federal Republic of Germany (West Germany), aligned with the United States, and the German Democratic Republic (East Germany), aligned with the U.S.S.R. The Berlin crisis also seemed to show that containment worked and thus strengthened U.S. resolve to maintain a strong European and U.S. military presence in western Europe. In 1949, the United States formed NATO (the North Atlantic Treaty Organization), an anti-Soviet military alliance of Western governments. In 1955, the Soviets countered by organizing the Warsaw Pact, a military alliance among the U.S.S.R. and its Communist satellites. In both political and military terms, most of Europe was divided into two hostile blocs.

The Cold War took shape in Europe, but it quickly spread around the globe, turning hot in East Asia. When Soviet-backed Communist North Korea invaded South Korea in 1950, President Truman swiftly sent U.S. troops. In the end, the Korean War was indecisive: the fragile truce agreed to in 1953 left Korea divided between a Communist north and a capitalist south. The war nonetheless showed that, though the superpowers might maintain a fragile peace in Europe, they were perfectly willing to engage in open conflict in non-Western territories.

By 1955, the Soviet-American confrontation had become an apparently permanent feature of world affairs. For the next thirty-five years, the superpowers would struggle to win political influence and territorial control and to achieve technological superiority. Cold War hostilities helped foster a nuclear arms race, a space race, and the computer revolution, all made possible by stunning advances in science and technology.