Vietnam War: The Easter Offensive begins after North Vietnamese forces cross into the Demilitarized Zone (DMZ) of South Vietnam.

The Easter Offensive, also known as the 1972 spring–summer offensive by North Vietnam, or the Red Fiery Summer as romanticized in South Vietnamese literature, was a military campaign conducted by the People's Army of Vietnam against the Army of the Republic of Vietnam and the United States military between 30 March and 22 October 1972, during the Vietnam War.

North Vietnam, officially the Democratic Republic of Vietnam, was a country in Southeast Asia from 1945 to 1976, with sovereignty fully recognized in 1954. A member of the communist Eastern Bloc, it opposed the French-supported State of Vietnam and later the Western-allied Republic of Vietnam. The DRV invaded Saigon in 1975 and ceased to exist the following year when it merged with the south to become the current Socialist Republic of Vietnam.

The Vietnamese Demilitarized Zone was a demilitarized zone at the 17th parallel in Quang Tri province that was the dividing line between North Vietnam and South Vietnam from 21 July 1954 to 2 July 1976, when Vietnam was officially divided into two de facto countries, which was two de jure military gathering areas supposed to be sustained in the short term after the First Indochina War.

South Vietnam, officially the Republic of Vietnam, was a country in Southeast Asia that existed from 1955 to 1975. It first garnered international recognition in 1949 as the associated State of Vietnam within the French Union, with its capital at Saigon. Since 1950, it was a member of the Western Bloc during the Cold War. Following the 1954 partition of Vietnam, it became known as South Vietnam and was established as 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. It was succeeded by the Republic of South Vietnam in 1975. In 1976, the Republic of South Vietnam and North Vietnam merged to form the Socialist Republic of Vietnam.