The U.S. entered into the Vietnam War in their fight to stop the spread of communism. China had close ties with communist North Vietnam and were afraid that communism would spread to the South, so the U.S. entered and provided support to the South Vietnamese.
Many Americans did not support the war on moral grounds, but the primarily reason was because people felt the war was an entanglement in a foreign civil war. Furthermore, they felt the war had no clear objective or endgame and that it was a waste of money, resources, and American lives. The war lasted twenty years, and resulted in America pulling out with nothing to show for it.
