North Vietnam, officially the Democratic Republic of Vietnam (DRV), was a socialist state in Southeast Asia that existed from 1945 to 1976.

During the August Revolution following World War II, Vietnamese communist revolutionary H Ch Minh, leader of the Vit Minh Front, declared independence on 2 September 1945, announcing the creation of the Democratic Republic of Vietnam. The Vit Minh ("League for the Independence of Vietnam"), led by communists, was created in 1941 and designed to appeal to a wider population than the Indochinese Communist Party could command.From the very beginning, the DRV regime sought to consolidate power by purging other nationalist movements. Meanwhile, France moved in to reassert its colonial dominance over Vietnam. After the communist-led Vit Minh severely eliminated non-communist nationalist organizations, the First Indochina War burst out between the Vit Minh and the French in December 1946. During this guerrilla war, the Vit Minh captured and controlled most of the rural areas in Vietnam which led to French defeat in 1954. The negotiations in the Geneva Conference that year ended the war and recognized Vietnamese independence. The Geneva Accords provisionally divided the country into a northern and a southern zone along the 17th parallel, stipulating general elections scheduled for July 1956 to "bring about the unification of Viet-Nam". The northern zone was controlled by the Democratic Republic of Vietnam and became commonly called North Vietnam, while the southern zone, under control of the de jure non-communist State of Vietnam was commonly called South Vietnam.

Supervision of the implementation of the Geneva Accords was the responsibility of an international commission consisting of India, Canada, and Poland, respectively representing the non-aligned, the non-communist, and the communist blocs. The United States, however, did not sign the Geneva Accords and stated that it "shall continue to seek to achieve unity through free elections supervised by the United Nations to ensure that they are conducted fairly". The State of Vietnam strongly opposed the partition of the country. In July 1955, its prime minister, Ng nh Dim, announced that South Vietnam would not participate in elections, claiming that the State of Vietnam had not signed the Geneva Accords and was therefore not bound by it, and raising concerns that an unfree election would occur under the communist regime in North Vietnam.Failure to unify the country by referendum led to the Vietnam War in 1955. The North Vietnamese People's Army of Vietnam and the South Vietnam-based Vit Cng guerrilla fought against the military of South Vietnam (by then the Republic of Vietnam) and were backed by their communist allies, mainly China and the Soviet Union. To prevent other countries from becoming communist in Southeast Asia, the United States intervened in the conflict along with other anti-communist forces from South Korea, Australia and Thailand, who heavily supported South Vietnam militarily. The conflict spread to neighboring countries and North Vietnam supported the Pathet Lao in Laos and the Khmer Rouge in Cambodia against their respective US-backed governments. By 1973 the United States and its allies had been forced to withdraw from the war, this left South Vietnam alone and it was swiftly overrun by the superior Northern forces.

The Vietnam War ended on 30 April 1975 and saw South Vietnam come under the control of a Provisional Revolutionary Government, which led to the reunification of Vietnam on 2 July 1976, creating the Socialist Republic of Vietnam of today. The expanded Socialist Republic retained North Vietnam's political culture under Soviet influence and continued its existing memberships in international organisations such as COMECON.

South Vietnam, officially the Republic of Vietnam (RVN; Vietnamese: Việt Nam Cộng Hòa; French: République du Viêt Nam), was a country that existed from 1955 to 1975, the period when the southern portion of Vietnam was a member of the Western Bloc during part of the Cold War. It first received international recognition in 1949 as the State of Vietnam within the French Union, with its capital at Saigon (renamed to Ho Chi Minh City in 1976), before becoming a republic in 1955. South Vietnam was bordered by North Vietnam to the north, Laos to the northwest, Cambodia to the southwest, and Thailand across the Gulf of Thailand to the southwest. Its sovereignty was recognized by the United States and 87 other nations, though it failed to gain admission into the United Nations as a result of a Soviet veto in 1957.The end of the Second World War saw anti-Japanese Việt Minh guerrilla forces, led by communist fighter Ho Chi Minh, proclaiming the establishment of the Democratic Republic of Vietnam in Hanoi in September 1945. In 1949, anti-communist politicians formed a rival government in Saigon led by former emperor Bảo Đại. A 1955 referendum on the state's future form of government was highly contested and resulted in the deposal of Bảo Đại by Prime Minister Ngô Đình Diệm, who proclaimed himself president of the new republic on 26 October 1955. After the 1954 Geneva Conference, it abandoned its claims to the northern part of the country and established its sovereignty over the southern half of Vietnam consisting of Cochinchina (Nam Kỳ) – a former French colony and parts of Annam (Trung Kỳ) – a former French protectorate. Diệm was killed in a military coup led by general Dương Văn Minh with help from the CIA in 1963, and a series of short-lived military governments followed. General Nguyễn Văn Thiệu then led the country after a US-encouraged civilian presidential election from 1967 until 1975.

The beginnings of the Vietnam War occurred in 1955 with an uprising by the newly organized National Liberation Front for South Vietnam (Việt Cộng), armed and supported by the North Vietnam, with backing mainly from China and the Soviet Union. Larger escalation of the insurgency occurred in 1965 with American intervention and the introduction of regular forces of Marines, followed by Army units to supplement the cadre of military advisors guiding the Southern armed forces. A regular bombing campaign over North Vietnam was conducted by offshore US Navy airplanes, warships, and aircraft carriers joined by Air Force squadrons through 1966 and 1967. Fighting peaked up to that point during the Tet Offensive of February 1968, when there were over a million South Vietnamese soldiers and 500,000 US soldiers in South Vietnam. What started as a guerrilla war eventually turned into a more conventional fight as the balance of power became equalized. An even larger, armored invasion from the North commenced during the Easter Offensive following US ground-forces withdrawal, and had nearly overran some major northern cities until beaten back.

Despite a truce agreement under the Paris Peace Accords, concluded in January 1973 after five years of on-and-off negotiations, fighting continued almost immediately afterwards. The regular North Vietnamese army and Việt-Cộng auxiliaries launched a major second combined-arms conventional invasion in 1975. Communist forces overran Saigon on 30 April 1975, marking the end of the Republic of Vietnam. On 2 July 1976, North Vietnam-controlled Provisional Revolutionary Government of the Republic of South Vietnam and the Democratic Republic of Vietnam (North Vietnam) merged to form the Socialist Republic of Vietnam.