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.

The Vietnam War (Vietnamese: Chiến tranh Việt Nam), also known as the Second Indochina War, was a conflict in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. It was the second of the Indochina Wars and was officially fought between North Vietnam and South Vietnam. North Vietnam was supported by the Soviet Union, China, and other communist allies; South Vietnam was supported by the United States and other anti-communist allies. The war is widely considered to be a Cold War-era proxy war. It lasted almost 20 years, with direct U.S. involvement ending in 1973. The conflict also spilled over into neighboring states, exacerbating the Laotian Civil War and the Cambodian Civil War, which ended with all three countries becoming communist states by 1975.

The conflict emerged from the First Indochina War between the French colonial government and a left-wing revolutionary movement, the Viet Minh. After the French military withdrawal from Indochina in 1954, the U.S. assumed financial and military support for the South Vietnamese state. The Việt Cộng (VC), a South Vietnamese common front under the direction of North Vietnam, initiated a guerrilla war in the south. North Vietnam had also invaded Laos in 1958 in support of insurgents, establishing the Ho Chi Minh Trail to supply and reinforce the Việt Cộng.: 16  By 1963, the North Vietnamese had sent 40,000 soldiers to fight in the south.: 16  U.S. involvement escalated under President John F. Kennedy through the MAAG program, from just under a thousand military advisors in 1959 to 23,000 in 1964.: 131 In the Gulf of Tonkin incident in August 1964, a U.S. destroyer clashed with North Vietnamese fast attack craft. In response, the U.S. Congress passed the Gulf of Tonkin Resolution and gave President Lyndon B. Johnson broad authority to increase U.S. military presence in Vietnam. Johnson ordered the deployment of combat units for the first time and increased troop levels to 184,000. The People's Army of Vietnam (PAVN) (also known as the North Vietnamese Army or NVA) engaged in more conventional warfare with U.S. and South Vietnamese forces (Army of the Republic of Vietnam (ARVN)). Despite little progress, the U.S. continued a significant build-up of forces. U.S. and South Vietnam forces relied on air superiority and overwhelming firepower to conduct search and destroy operations, involving ground forces, artillery, and airstrikes. The U.S. also conducted a large-scale strategic bombing campaign against North Vietnam.: 371–4 The communist Tet Offensive throughout 1968 caused U.S. domestic support for the war to fade. The VC sustained heavy losses during the Offensive and subsequent U.S.-ARVN operations.: 481  The CIA's Phoenix Program further degraded the VC's membership and capabilities. By the end of the year, the VC insurgents held almost no territory in South Vietnam, and their recruitment dropped by over 80%, signifying a drastic reduction in guerrilla operations, necessitating increased use of PAVN regular soldiers from the north. In 1969, North Vietnam declared a Provisional Revolutionary Government (the PRG) in the south to give the reduced VC a more international stature, but from then on, they were sidelined as PAVN forces began more conventional combined arms warfare. By 1970, over 70% of communist troops in the south were northerners, and southern-dominated VC units no longer existed. Operations crossed national borders: North Vietnam used Laos as a supply route early on, while Cambodia was also used starting in 1967; the U.S. bombed the Laotian route starting in 1964, and the Cambodian route in 1969. The deposing of the monarch Norodom Sihanouk by the Cambodian National Assembly resulted in a PAVN invasion of the country at the request of the Khmer Rouge, escalating the Cambodian Civil War and resulting in a U.S.-ARVN counter-invasion.

In 1969, following the election of U.S. President Richard Nixon, a policy of "Vietnamization" began, which saw the conflict fought by an expanded ARVN, with U.S. forces sidelined and increasingly demoralized by domestic opposition and reduced recruitment. U.S. ground forces had largely withdrawn by early 1972 and support was limited to air support, artillery support, advisers, and materiel shipments. The ARVN, with U.S. support, stopped the first and largest mechanized PAVN offensive during the Easter Offensive of 1972. The offensive failed to subdue South Vietnam, but the ARVN itself failed to recapture all lost territory, leaving its military situation difficult. The Paris Peace Accords of January 1973 saw all U.S. forces withdrawn; the Case–Church Amendment, passed by the U.S. Congress on 15 August 1973, officially ended direct U.S. military involvement.: 457  The Peace Accords were broken almost immediately, and fighting continued for two more years. Phnom Penh fell to the Khmer Rouge on 17 April 1975, while the 1975 Spring Offensive saw the Fall of Saigon by the PAVN on 30 April; this marked the end of the war, and North and South Vietnam were reunified the following year.

By 1970, the ARVN was the world's fourth largest army, and the PAVN was not far behind with approximately one million regular soldiers.: 770  The war exacted an enormous human cost: estimates of the number of Vietnamese soldiers and civilians killed range from 966,000 to 3 million. Some 275,000–310,000 Cambodians, 20,000–62,000 Laotians, and 58,220 U.S. service members also died in the conflict, and a further 1,626 remain missing in action.The Sino-Soviet split re-emerged following the lull during the Vietnam War. Conflict between North Vietnam and its Cambodian allies in the Royal Government of the National Union of Kampuchea, and the newly formed Democratic Kampuchea began almost immediately in a series of border raids by the Khmer Rouge, eventually escalating into the Cambodian–Vietnamese War. Chinese forces directly invaded Vietnam in the Sino-Vietnamese War, with subsequent border conflicts lasting until 1991. The unified Vietnam fought insurgencies in all three countries. The end of the war and resumption of the Third Indochina War would precipitate the Vietnamese boat people and the larger Indochina refugee crisis, which saw millions of refugees leave Indochina (mainly southern Vietnam), an estimated 250,000 of whom perished at sea. Within the U.S., the war gave rise to what was referred to as Vietnam Syndrome, a public aversion to American overseas military involvements, which together with the Watergate scandal contributed to the crisis of confidence that affected America throughout the 1970s.