The Vietnam War occurred in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. It was the second of the Indochina Wars and was officially fought between North Vietnam and the government of South Vietnam. The North Vietnamese army was supported by the Soviet Union, China and other communist allies and the South Vietnamese army was supported by the United States, South Korea, Australia, Thailand and other anti-communist allies. While the Viet Cong fought a guerrilla war against anti-communist forces in the region, the North Vietnamese Army (NVA), engaged in more conventional warfare, at times committing large units to battle. As the war continued, the military actions of the Viet Cong decreased as the role and engagement of the NVA grew. U.S. and South Vietnamese forces relied on air superiority and overwhelming firepower to conduct search and destroy operations, involving ground forces, artillery, and airstrikes. The North Vietnamese government and the Viet Cong were fighting to reunify Vietnam, viewing the conflict as a colonial war and a continuation of the First Indochina War against forces from France and the United States. The U.S. government viewed its involvement in the war as a way to prevent a communist takeover of South Vietnam, with a wider aim of stopping the spread of communism worldwide.