Because they didn't have enough time to leave Vietnam during the Vietnam War
Begin with websites: Statistics about the Vietnam War & Vietnam War Time-Line
Japan left Vietnam because the US won the Vietnam War. The US effectively kicked them out of the area. This was preventing China from invading Vietnam as well.
1961 is the year most accepted by current historians.
President Eisenhower sent US troops to Vietnam in 1955, President Ford pulled out the last US troops in 1975.
US POWs still surviving in North Vietnam were released to the US in 1973; the vast majority of them were US Airmen who had been shot down during the air war over North Vietnam.
The United States went into war with Vietnam in the year 1965.
US war in RVN commenced in 1955. US war against North Vietnam commenced in 1964.
We were at war with Vietnam because they disagreed with us about something.
A US Vietnam War veteran in the year 2008 could be around the age of 50. There were US Marines/US Air Force/US Navy Aircrewmen younger than 19 years old in Vietnam in 1975.
The United States withdrew from Vietnam on March 29, 1973.
Vietnam