The following is a chronology of the anti-US war that ended with the liberation of southern Vietnam and re-unification of the country on April 30, 1975.

• July 20, 1954: The United States refuses to sign the Geneva Agreement on peace in Vietnam. Instead, America increases its political and military involvement in Southern Vietnam-supporting the Sai Gon regime, undermining the agreement, and rejecting elections for national reunification. As a result, on May 19, 1959, President Ho Chi Minh orders Vietnamese armed forces to open a secret supply network along the Truong Son range to provide the southern liberation forces with reinforcements and supplies. The route, with more than 23,000km of mountain roads and paths, later becomes famous as the Ho Chi Minh Trail.

• December 20, 1960: The establishment of the National Liberation Front of South Vietnam (NLF). It is a resistance movement in Southern Vietnam to fight against US intervention and the Ngo Dinh Diem administration.

• August 5, 1964: US aircraft launch their first strikes against Northern Vietnam under the pretext of the Vinh Bac Bo (Gulf of Tonkin) incident, during which the Vietnam Navy allegedly attacked the US warship Maddox. The US aerial strikes against Northern Vietnam continue for eight years.

• May 27, 1965: The first clashes between the Vietnamese liberation army and US troops begin 80 days after US forces landed in Southern Vietnam. One US company is put out of action at an outpost on central Quang Nam province's Nui Thanh Mountain.

• January 30 - March 31, 1968: The Tet Mau Than offensive is launched throughout Southern Vietnam, serving a strategic blow to Washington and forcing President L. B. Johnson to enter talks with Hanoi to bring the conflict to an end. One year later the first round of four-party talks on Vietnam opens in Paris.

• June 8, 1969: US President Richard Nixon declares the first withdrawal of 25,000 US troops from Southern Vietnam, and begins a scheme of Vietnamising the war.

• March 1970: The US expands the war to the entire Indochinese peninsula, as American and Sai Gon troops are sent to Cambodia in an attempt to wipe out Vietnamese liberation bases in the country.

• February 27, 1973: When B-52 bomber strikes against Hanoi fail, the US signs the Paris Agreement on Vietnam and begins withdrawing all American troops from Southern Vietnam.

• March 10, 1975: The liberation forces launch surprise attacks against Buon Ma Thuot, following a series of diversionary moves to distract the Sai Gon army from the Central Highlands (Tay Nguyen) township. The fall of Buon Ma Thuot the next day triggers a domino effect on the deteriorating morale of the Sai Gon armed forces, which, two weeks later, flee to the central coast.

• March 29, 1975: Da Nang, the second largest city in Southern Vietnam, is overrun after two days of attacks by the liberation forces. Four days earlier they also take Hue, 80km north of Da Nang.

• April 14, 1975: The quick defeat of the Sai Gon forces prompts the Politburo to make a historic decision: it launches the Ho Chi Minh Campaign to liberate Sai Gon and the rest of Southern Vietnam.

• April 21, 1975: The liberation forces' fast advance towards Sai Gon, which is already engulfed in political chaos, forces Sai Gon President Nguyen Van Thieu to resign, making way for Tran Van Huong, who six days later transfers the power to Duong Van Minh.

• April 30, 1975: The liberation forces swoop down on Sai Gon from all four directions, forcing the US-backed administration to surrender unconditionally. The Ho Chi Minh Campaign ends in total victory after 55 days of fighting. (VNA)