Vietnam was occupied by Japan during WWII and after their defeat rebel leader Ho-Chi Minh proclaimed the republic of Vietnam. Vietnam defeated the French in 1954, Vietnam was divided in two at the 17th longitude. The regime in N-Vietnam was supported by the liberation front of Vietnam and the S-Vietnamese regime was supported by the USA. The communist north was to some extent supported by other communist states such as China and the Soviet Union. The north supported Vietcong tried to take the whole country.
The US feared that a communist takeover would create tensions with Russia and China and communism was greatly feared in the US at that time. Although the United States had pushed a great number of troops into Vietnam since the 1950s, they could not overpower the North Vietnamese guerrilla soldiers who were great tacticians and fought fiercely against the less motivated American soldiers who were faced with an alien environment. The lack of a clear front also made it difficult for the well-organized American army to fight the Vietnamese that could hide in the jungles and tiny villages around the countryside. The Americans suffered one of their greatest military losses in a war they had not lost but had failed to win. The created difficulties for the Americans as few at home supported the American involvement. The US made great efforts to withdraw and in 1973 the Americans left Vietnam for good. 2.5 million had been killed on both sides and millions more were affected by injuries. In 1976 Vietnam was officially joined together as one communist state.