The United States was involved in several international crises in the 1960's despite continued efforts to ease Cold War tensions. In 1961 East Germany, acting on Soviet instructions, built a wall between East and West Berlin to halt the flow of East German refugees to West Germany. This action produced a crisis between the Soviet Union and the United States over Western rights in Berlin, which since World War II had been occupied by Soviet, American, British, and French forces. There were fears of a major confrontation but the crisis was eased by diplomatic measures.
In 1961 Cuban exiles, trained with the aid of the United States, invaded their homeland at the Bay of Pigs in an unsuccessful attempt to overthrow the Communist regime of Fidel Castro. Cuba was again an issue in 1962, when President Kennedy forced the Soviet Union to remove missiles it had sent there. After the crisis—which was so serious that it might have led to nuclear conflict between the two superpowers—Soviet-American relations improved. A limited nuclear test-ban treaty was negotiated in 1963 and consular and space treaties in 1967.
United States ties with Latin America were strengthened by the Alliance for Progress in 1961. However, relations were strained for a time following President Johnson's dispatch of troops to the Dominican Republic in 1965 to prevent seizure of that country's government by Communist revolutionaries.
United States involvement in Southeast Asia expanded steadily in the 1960's. In 1962, in order to prevent further Communist penetration of Laos, the United States participated in negotiations that led to an international agreement to guarantee the neutrality of that country. Economic and military aid to South Vietnam to fight Communist guerrillas, begun in the 1950's, eventually led to President Johnson's dispatch of large numbers of American combat troops in 1965. The continued "escalation" (expansion) of the Vietnamese War caused worldwide concern and provoked an antiwar movement in the United States. Despite the efforts that began in 1968 to negotiate a settlement, the war continued.