Though the last of the U. S. combat troops left Vietnam in 1973, the war between North Vietnam and South Vietnam continued. In March 1975, North Vietnam attacked the South in the Central Highlands. Driving onward, the North continued its invasion, and in April, nearly 300,000 North Vietnamese troops were in the South. The North was poised to attack Saigon, South Vietnam's capital city. Top priority for American leaders became the evacuation of all Americans posted in Saigon. Chaos filled the streets and soon the only way out was by helicopter.