In 1972, the North Vietnamese launched a massive invasion of South Vietnam. The South Vietnamese forces reeled under the attack, but eventually prevailed with the help of U.S. airpower. After extensive negotiations and the bombing of North Vietnam in December 1972, the Paris Peace Accords were signed in January 1973. Under the provisions of the Accords, U.S. forces were completely withdrawn. Unfortunately, this did not end the war for the Vietnamese and the fighting continued until April 1975 when Saigon fell to the communists.