The US got involved in the Vietnam War because it did not want another country going to communism (and therefore the Soviet sphere of influence) after what happened in China. The North Vietnamese government and the Viet Cong were fighting to reunify Vietnam. U.S. government viewed its involvement in the war as a way to prevent a communist takeover of South Vietnam. This was part of the domino theory of a wider containment policy, with the stated aim of stopping the spread of communism.
