The Vietnam War was the United State's attempt to stop communism from spreading across Eastern Asia. At the time it was believed that if Vietnam fell to communism, a Domino Effect would occur, and many states around Vietnam would fall to communism. While the US sent many troops, more than 500,000 by 1965, the war effort ended up being pointless and Vietnam fell to communism in the 1970s. The US left Vietnam in 1973, leaving South Vietnam to fall by 1975.