1974
Thieu Announces Renewal of War
Report Cites Damage to Vietnam Ecology: According to a report issued by The National Academy of Science, use of chemical herbicides during the war caused long-term damage to the ecology of Vietnam. Subsequent inquiries will focus on the connection between certain herbicides, particularly Agent Orange, and widespread reports of cancer, skin disease, and other disorders on the part of individuals exposed to them.
Communists Take Mekong Delta Territory
Nixon Resigns
Communists Plan Major Offensive: With North Vietnamese forces in the South believed to be at their highest levels ever, South Vietnamese leaders gird themselves for an expected Communist offensive of significant proportions.
1975
Communist Forces Capture Phuoc Long Province: The South Vietnamese Army loses twenty planes in a failed effort to defend Phuoc Long, a key province just north of Saigon. North Vietnamese leaders interpret the US's complete lack of response to the siege as an indication that they could move more aggressively in the South.
Hue Falls to Communists
Communists Take Aim at Saigon: The North Vietnamese initiate the Ho Chi Minh Campaign -- a concerted effort to "liberate" Saigon. Under the command of General Dung, the NVA sets out to capture Saigon by late April, in advance of the rainy season.
Ford Calls Vietnam War "Finished": Anticipating the fall of Saigon to Communist forces, US President Gerald Ford, speaking in New Orleans, announces that as far as the US is concerned, the Vietnam War is "finished."
Last Americans Evacuate as Saigon Falls to Communists: South Vietnamese President Duong Van Minh delivers an unconditional surrender to the Communists in the early hours of April 30. North Vietnamese Colonel Bui Tin accepts the surrender and assures Minh that, "...Only the Americans have been beaten. If you are patriots, consider this a moment of joy." As the few remaining Americans evacuate Saigon, the last two US servicemen to die in Vietnam are killed when their helicopter crashes.
http://www.english.uiuc.edu/maps/vietnam/timeline.htm