to.help the French originally,in,a u n police action,Kennedy was going to get us out he got killed and Johnson bought stock in munitions and Boeing aircraft,escalated the war and got rich,but i digress,nam, was a French colony,the communist came in and were beating the French so the united nations took over but we did the heavy lifting
The most probable reason as to why the America fight in Vietnam is because they attempted to prevent the spread of Communism. Communists backed terrorists in Europe and Africa, South America and the Arabs in the Middle East.
To be very technical, It was part of the Cold War. Communism was becoming more popular in smaller and poorer countries, and America and it's Democratic allies were worried that Russia(During the USSR period) would cause a Domino effect if it takes control(Really just assisting them to change to a communist government) of Vietnam. The Domino effect is the theory that if one country becomes communist, all nearby countries will also do the same. There was already a lot of communist countries in that section of the world, America feared that the USSR would gain extreme power and resources. So, we assisted the lower democratic section of Vietnam, and the USSR gave support to the northern communist government.
The way it was explained to me by a man who was there from 1965 until the time we pulled out was that a large percentage of world trade went through that area and the Communists were trying to defeat Capitalism by controlling commerce in that area. That was his view. I don't know if he was right or not but it made sense to me at the time. Obviously Capitalism did survive after we pulled out so I don't know but when we did pull out of that area it left a lot of people helpless and the Khmer Rouge led by Pol Pot was able to commit great atrocities and genocide in Cambodia. I don't know if we should have been there or not but it seems to me that if you are going to go to war you should go all out and win the war in the shortest time possible or don't bother. A lot of Americans died there and a lot of Americans (including my cousin who was like a big brother to me) suffered as a result of our involvement. Australia also sent troops and paid a price. I would hate to think it was all for nothing but maybe it was. We should still honor those who sacrificed and served. When the country called they answered.