In 1965, Johnson sent the first US combat troops into Vietnam and they left in 1973, accomplishing nothing. The United States was unable to defeat communism in South-East Asia between those years because of their ineptitude, and the superior tactics of the Viet Cong.
There were many problems that the Americans faced. Firstly, they didn't get along with the Vietnamese people. The Americans disliked the very people that they were supposedly helping, all people were treated the same, Viet Cong or not. One US marine said: "If they weren't pro Viet Cong before we got there, they sure as well were by the time we left." An example of this hatred is the My Lai massacre in March 1968 were over 300 civilians were killed. The Americans also had a lax way of life compared to the Communists who only had the basics. Americans were lavished with comfort foods and facilities, at a peak there were over 150 baseball courts, 70 swimming pools and 40 ice-cream plants, cigarettes and bear were also airdropped mid-siege. On top of this there were massive drugs and sex problems, in 1971 only 5000 troops were treated for combat wounds but 20,000 for serious drug abuse. The way the Americans had things did not help, they had a massive lack of discipline.
US military tactics were also incompetent. One of the most prominent approaches was Operation Rolling Thunder which ended in a strategic US failure. Rolling Thunder was the name for the aerial bombardment against North Vietnam, the US dropped more bombs in Vietnam than they did in WWII. There were complications from the start as the US Air Force was limited as to where it could bomb so it didn't provoke a Soviet or Chinese response, this was contrary to what the Hawks wanted in Congress – to show the US military power. Johnson rarely consulted with military chiefs in what targets to bomb. The unpreparedness of the Air Force was exposed during this operation, aircrafts and pilots had been geared for strategic ops against the USSR, not conventional war.