In general, we can account for the growing American military involvement in Vietnam in these years by looking at the shortcomings of the South Vietnamese military and government. Starting from this foundation, American involvement also grew due to “mission creep” inertia and a sense that Vietnam was important to American prestige in the world.
In 1961, the US was not very involved in Vietnam militarily. President Kennedy sent Green Berets to South Vietnam to help train the Vietnamese military, but there was no large-scale American involvement. Instead, the US was content to try to support the regime of Ngo Dinh Diem. As the ‘60s wore on, however, it became clear that Diem’s government was very weak. Diem himself was not well-liked by the people and his government lacked popular support. The Vietnamese military was not well-trained and, more importantly, was not very motivated to fight for the Diem government. These things meant that the non-communists in South Vietnam were showing many signs of weakness. Because of this weakness, the US felt that it had to be more and more involved to prevent South Vietnamese weaknesses from leading to the “loss” of that country.
Once this happened, inertia took over. Relatively low levels of American involvement led to greater levels. For example, when we put air combat units in Vietnam, we soon decided that we had to send ground troops to defend their bases. The military leaders then decided that the ground troops should go out and fight aggressively rather than simply staying in defensive positions around bases. These kinds of “mission creep” helped to increase our involvement in the war. This process culminated in the Gulf of Tonkin Resolution, which led to the deployment of hundreds of thousands of American military personnel in Vietnam. At the same time, American prestige became wrapped up in Vietnam. If we were taking over more and more of the waging of the war we had to win it or else we would look weak in the eyes of the world (so the thinking went). This caused the US government to pour more and more troops into the country in an attempt to win the war and maintain America’s stature in the eyes of the world.
During the early 1960s, US military involvement in Vietnam grew as it became clear that the South Vietnamese government was not strong enough to fight on its own and as Vietnam became more important to American prestige.