In 1947, the United States began to implement the doctrine of containment that would guide foreign policy for the next four decades. It was not an easy transition; Americans approved of taking a hard line against the Soviet Union but wanted to keep their soldiers and tax dollars at home. In addition to selling containment to the public, Truman had to gain the support of a Republican-controlled Congress.

Crises in two Mediterranean countries triggered the implementation of containment. In February 1947, Britain informed the United States that its crippled economy could no longer sustain military assistance to Greece, where the autocratic government faced a leftist uprising, and to Turkey, which was trying to resist Soviet pressures. Truman promptly sought congressional authority to send the two countries military and economic aid. Meeting with congressional leaders, Undersecretary of State Dean Acheson predicted that if Greece and Turkey fell, communism would soon consume three-fourths of the world. After a stunned silence, Michigan senator Arthur Vandenberg, the Republican foreign policy leader, warned that to get approval, Truman would have to “scare hell out of the country.”

Truman did just that. He warned that if Greece fell to the rebels, “confusion and disorder might well spread throughout the entire Middle East” and then create instability in Europe. According to what came to be called the Truman Doctrine, the United States must not only resist Soviet military power but also “support free peoples who are resisting attempted subjugation by armed minorities or by outside pressures.” The president failed to convince some liberal members of Congress who wanted the United States to work through the United Nations and opposed propping up the authoritarian Greek government. But the administration won the day, setting a precedent for forty years of Cold War interventions that would aid any kind of government if the only alternative appeared to be communism. A much larger assistance program for Europe followed aid to Greece and Turkey. In May 1947, Acheson described a war-ravaged Western Europe, with “factories destroyed, fields impoverished, transportation systems wrecked, populations scattered and on the borderline of starvation.” American citizens were sending generous amounts of private aid, but Europe needed large-scale assistance to keep desperate citizens from turning to socialism or communism.

In March 1948, Congress approved such assistance, which came to be called the Marshall Plan, after Secretary of State George C. Marshall, who proposed it. Over the next five years, the United States spent $13 billion ($117 billion in 2010 dollars) to restore the economies of sixteen Western European nations. Marshall invited all European nations and the Soviet Union to cooperate in a request for aid, but the Soviets objected to the American terms of free trade and financial disclosure. They ordered their Eastern European satellites to reject the offer.

Humanitarian impulses as well as the goal of keeping Western Europe free of communism drove the adoption of this enormous aid program. But the Marshall Plan also helped boost the U.S. economy because the participating European nations spent most of the dollars to buy American products and Europe’s economic recovery created new markets and opportunities for American investment. And by insisting that the recipient nations work together, the Marshall Plan marked the first step toward the European Union.

In February 1948, the Soviets staged a brutal coup and installed a Communist regime in Czechoslovakia, the last democracy left in Eastern Europe. Next, Stalin threatened Western access to Berlin. That former capital of Germany lay within Soviet-controlled East Germany, but all four Allies jointly occupied it. As the Western Allies moved to organize West Germany as a separate nation, the Soviets retaliated by blocking roads and rail lines between West Germany and the Western-held sections of Berlin, cutting off food, fuel, and other essentials to two million inhabitants. “We stay in Berlin, period,” Truman vowed. To avoid a confrontation with Soviet troops, for nearly a year U.S. and British pilots airlifted 2.3 million tons of goods to sustain the West Berliners. Stalin hesitated to shoot down these cargo planes, and in 1949 he lifted the blockade. The city was then divided into East Berlin, under Soviet control, and West Berlin, which became part of West Germany.