Who was the main US ally in the Vietnam War?

The main US ally in the Vietnam War was South Vietnam. This relationship was foundational to U.S. military, political, and economic efforts in the conflict. South Vietnam, officially known as the Republic of Vietnam, was established in 1955 and was recognized by the United States as a legitimate government opposing the communist North Vietnam. The U.S. provided extensive support, including military aid and personnel, in an effort to bolster the South Vietnamese government against the communist forces led by the North.

Support for South Vietnam was part of the broader U.S. strategy of containment during the Cold War, aiming to prevent the spread of communism in Southeast Asia. The alignment with South Vietnam was characterized by significant troop deployments and substantial financial assistance, which underscored the importance of this alliance for U.S. foreign policy at the time.