Why did the USA withdraw from Vietnam?

Timeline of Vietnam War

The Vietnam Peace Treaty

Many believe that the US signed the Treaty to save face. They had been involved in the war for over a decade and despite their superior weaponry, had been largely unsuccessful.

Before the last US troops had left, North Vietnamese forces had already violated the Treaty and resumption of full-scale war had already began by early 1974. By the end of 1974, South Vietnam reported that 80,000 soldiers and civilians had been killed. This meant it was the deadliest battle of the Vietnam War.