A country of southeast Asia in eastern Indochina on the South China Sea. It comprises the historical regions of Tonkin, Annam, and Cochin China, much of which was under Chinese control from the 3rd century BC to the 15th century AD. Portuguese traders arrived in 1535, and the area came under French influence in the mid-19th century as part of French Indochina. After the fall of the French garrison at Dien Bien Phu in 1954, it was partitioned into North Vietnam and South Vietnam. The Vietnam War (1959-1975) grew out of the attempt by Communist Vietcong guerrillas backed by North Vietnam to overthrow the US-supported regime in the south. The South Vietnamese government collapsed in 1975, and the country was reunited in 1976. Hanoi is the capital and Ho Chi Minh City the largest city.