Following a Japanese occupation in the 1940s, the Vietnamese fought French rule in the First Indochina War, eventually expelling the French in 1954. Thereafter, Vietnam was divided politically into two rival states, North and South Vietnam.ietnam's independence was gradually eroded by France – aided by large Catholic militias – in a series of military conquests between 1859 and 1885. In 1862, the southern third of the country became the French colony of Cochinchina.