History.com: Steps Leading to the Fall of Saigon and the Final, Chaotic Airlifts

The conflict in Vietnam ended in 1975 with the largest helicopter evacuation of its kind in history. What led to the fall of Saigon? Although the United States had withdrawn its combat forces from Vietnam after the signing of the Paris Peace Accords in 1973, approximately 5,000 Americans including diplomats, marine guards, contractors and Central Intelligence Agency employees remained. North Vietnam never intended to abide by the 1973 agreement - its ultimate mission was to unify the country.