The correct answer is "The Vietnam War".
The Vietnam War, also known as the Second Indochine War, started on November 1st, 1955 and lasted until April 30th with the fall of Saigon. The country was politically divided into 2 territories. North and South Vietnam. The northern part was ruled by a communist regime and aided by China. On the other hand, the southern part was supported by the United States.
At the end of the War, the United States decided to ultimately withdraw, ceding the territory to the communist regime of Northern Vietnam.