Following the French defeat at Dien Bien Phu in 1954, Vietnam was divided at the 17th parallel. The northern Democratic Republic of Vietnam was a communist regime, and the southern Republic of Vietnam was supported by the United States in order to stop the spread of communism. American financial and military support increased throughout the 1950s, and especially the early 1960s. In 1964 the United States claimed that the North Vietnamese had attacked two U.S. destroyers in the Gulf of Tonkin, and Congress gave President Lyndon B. Johnson the authority to take all necessary measures. U.S. troop levels reached more than 500,000 by 1968. American units engaged in brutal combat against communist rebels and North Vietnamese forces. American forces remained in South Vietnam until 1973. In 1975 Saigon, the Republic of Vietnam’s capital, fell to the Viet Cong, and Vietnam was reunited under communist rule. Over 58,000 Americans died in the conflict, and tens of thousands more suffered physical and emotional wounds.