A key outpost during the Vietnam War, the city of Dong Ha and the surrounding area marked the northern border of South Vietnam, on the Vietnamese DMZ (demilitarized zone). As a result, the U.S. Marine Corps built its Combat Base at Dong Ha, within easy striking distance of North Vietnam.
On March 30-31, 1972, the North Vietnamese forces struck in a major surprise invasion of the South called the Easter Offensive, and overran Dong Ha. The fighting would continue in South Vietnam through October, although the North Vietnamese forces' momentum was broken in June when they lost the city of An Loc.
Logically, since Dong Ha was closest to North Vietnamese territory, it was among the last cities liberated as the southerners and US troops pushed the North Vietnamese back in the fall of 1972. It also was among the first to fall again in the final days of the war, after the U.S. pulled out and left South Vietnam to its fate.