Modern Vietnam was born in 1945 with the proclamation of independence from France. After a long war, independence was achieved in 1954, but the country immediately split into two independent states: the communist North Viet Nam, and the anti-communist South Viet Nam.
The United States became heavily involved in the Vietnam War, backing the south. North Viet Nam won the war in 1975 and the following year the country re-unified as the Socialist Republic of Vietnam.
Vietnam on Wikipedia