Final answer:
Following the U.S. withdrawal in 1973, South Vietnam fell to the North Vietnamese Communists in 1975, leading to the unification of Vietnam under a Communist regime.
Step-by-step explanation:
The withdrawal of U.S. forces from Vietnam in 1973 followed a ceasefire agreed upon at the Paris peace conference.
Despite this ceasefire, the withdrawal was later followed by the collapse of South Vietnam. In 1975, after a full-scale invasion, North Vietnamese Communists overran South Vietnamese defenses, leading to the fall of Saigon and the eventual takeover of all of Indochina.
The entire region, including Laos, Cambodia, and Vietnam, became unified under a Communist regime, marking the end of the Vietnam War, a conflict that had deeply affected the region's history and international relations.