The belief that they needed to stop the spread of communism in south-east Asia was called the domino theory it played an important part in the American way of thinking about the affairs of Vietnam. they thought if they could stop Vietnam from becoming communist then they could stop it from spreading into other countries in the surrounding area this made the US want to become more involved to make sure that other countries were safe from communism.
Before Dien Bien Phu the French were able to stop Vietnam from becoming communist and according to the Domino theory the rest of
South-east Asia as well. But when the French were forced to withdraw there was nothing to stop Vietnam from turning communist so the US wanted to become more involved to make sure that it did not.
In the Geneva conference an agreement was signed splitting Vietnam into North and South and election would be held two years later electing one ruler for all Vietnam. These elections never took place because Diem and the US believed that Ho Chi Minh and the communists would win. The US was involved at the Geneva conference but refused to sign it.
After the French withdrew from Vietnam the US sent military advisers to
South Vietnam and gave economic aid and modern weapons to make sure the people of the south stayed Pro-western and Anti-Communist, the advisers were used to train the ARVN. diems rooting out of all former Vietminh members made him unpopular with his people but as an anti-Communist he kept the support of the USA.
Even with US support Diem still made mistakes. His strategic hamlets idea made him even more unpopular because the villagers didn’t want to leave the land they had farmed for centuries. Diem took little notice of protests including the public suicide of the Buddhist monk Quang Duc who set fire to himself on the street but president Kennedy was deeply affected by it and became increasingly reluctant to support the Diem regime.
The US knew before it happened about the assassination of Diem (the CIA was probably involved) but did nothing to stop it because they knew diem was very unpopular and that they too would be unpopular if they continued
to be seen as supporting his actions. only three weeks later Kennedy himself was assassinated.
Kennedy’s successor, Johnson, didn’t believe a war in Vietnam would be worth fighting but they could not leave now so he decided to try to get the war over quickly which would mean a huge increase in involvement and to send in many more troops. Unlike Johnson, Kennedy always tried to keep the level of military support to a minimum.
In south Vietnam the Vietcong was supported by the communists in the north it fought the US forces and the ARVN. Its guerrilla tactics were alarmingly successful as it had the support of many of the peasants in the country and control of the countryside. The success of the Vietcong led to a huge increase in the numbers of military ‘advisers’ and involvement. The number of advisers grew from 685 in 1961 to 16,000 in November 1963.
When US ships were attacked twice in the gulf of Tonkin, Johnson was given the right to fight a war in South-east Asia as he saw fit. Later the US
was attacked at a base at Pleiku and in it 9 men were killed and 67 Americans were wounded. This led to Operation Rolling Thunder and a huge increase of involvement. Soon after The US sent in more troops and the USA was now fully involved in a war which would involve them for the next 8 years.
In 1954 the USA supported the french colonial claims in French Indo-china against the Vietminh and within 11 years the US had become involved in fighting their own war against the Vietcong and NVA. As the situation in Vietnam worsened the US became more and more involved.
Events including Diems assassination, the Gulf of Tonkin and Pleiku all increased US involvement but overall the main cause of the USA becoming involved in the first place was the Americans fear, hatred and obsession with stopping the spread of communism.
