U.S. involvement in Vietnam occurred within and because of the larger context of the Cold War between the United States and the Soviet Union. Immediately after World War II, tensions between the United States and USSR escalated, as Soviet forces occupied nearly all of Eastern Europe and set up Communist governments there as a buffer between the Soviet Union and the capitalist West. In 1946, British prime minister Winston Churchill famously railed against the USSR in his “iron curtain” speech, which lamented the sudden wall of secrecy that had gone up between Eastern and Western Europe.
In 1947, U.S. State Department analyst George F. Kennan argued that the USSR was not likely to make any rash moves and that the United States could keep Communism from spreading simply by deterring Soviet expansion at critical points, mostly in Europe, over the long term. This policy of containment became extraordinarily influential in the U.S. government and became the basis of U.S. policy for much of the Cold War.
Three major events in 1948 and 1949 brought the American fear of Communism to a fever pitch. First, the USSR, which controlled East Germany, attempted to drive U.S., British, and French forces out of West Berlin by cutting off all outside access to the city. The United States responded to this blockade with the Berlin airlift over the winter of 1948–1949, dropping crucial supplies into West Berlin until the Soviet Union relented. Then, in August 1949, the USSR successfully tested its first atomic bomb. Finally, in October 1949, after years of civil war, the Nationalist government of China fell to the Communist forces of Mao Zedong. The combined force of these three events plunged the United States into a deep paranoia and fear that Communists would take over the world and might even be plotting secret operations in the United States.
In this environment of alarm, national security advisors of U.S. president Harry S Truman wrote an influential memo called NSC-68 , which advocated a tremendous increase in military spending to finance a massive military buildup, hoping to deter Soviet aggression. Following the policy outlined by this document, the United States became increasingly concerned with Communist expansion anywhere, not just at the critical points that Kennan had identified. Combined with the beginning of the Korean War in 1950, NSC-68 encouraged President Truman to begin a rapid buildup of the U.S. military.
After the fall of Dien Bien Phu in 1954, Truman’s successor, President Dwight D. Eisenhower, gave a speech that would soon become famous and important as an outline of U.S. Cold War policy. In the speech, Eisenhower drew on Kennan’s previously articulated containment policy but went a step further in describing what became known as the domino theory. Eisenhower stated that the United States needed not only to contain the USSR at critical locations but in all locations, for if one nation became Communist, its neighbors were likely to turn Communist as well, falling like a row of dominoes.
As a result of the domino theory, U.S. policy makers began to see Vietnam as extremely important. If Vietnam became Communist, domino-theory logic held that all of Indochina, and perhaps even all of Southeast Asia, might become Communist. Well aware of the popularity of Ho Chi Minh and his Viet Minh associates in both North and South Vietnam, U.S. leaders feared that the free elections promised at the Geneva Conference, which were scheduled to occur in 1956, would result in a unified, Communist Vietnam.