The US wanted to get the war started. Remember the incident in the Gulf of Tonkin. The US claimed that the North Vietnamese shot unprovokedly at a US ship. This made big news in the US. Based on this incident, I forgot either Kenedy or Lyndon Johnson went on national television vowed to take appropriate military action. So the US military build up in South Vietnam began. Years later in his own book, Robert McNamarra admitted to the North Vietnamese General Giap that the US made up this story so it could began the war. Nothing happened at the Gulf of Tonkin. You should read his book. I believe the name of the book is “Inretrospect”.
I am still puzzled and baffled by the notion that South Vietnam was a fake. Can we get serious for a second?. People have lived in that land for thousands of years before the French arrived. They still do. Irrespective of what happened at the Geneva agreement in 1954, people and cultures had existed in what was then declared as South Vietnam. The Nguyen dynasty had ruled that land. And there were others that ruled before them. It’s laughable to assert that the land where these people had lived was an invention of foreigners.
Whether or not the South Vietnamese government or its military peformed well another issue altogether. In my judgment, the government was highly corrupted and the military did not perform well at all. They could have and should have done much better, but they did not. Keep in mind. The Vietnamization process did not start until after Nixon took the presidency. This means that not until about 1969 that the training and the recruitment of the South Vietnamese military actually began. The US ended its military engagement in 1973 and the South Vietnamese fought on until 1975. Keep in mind South Vietnamese had no experience in warfare as the North Vietnamese did. The North had fought the Japanese, the French and the Americans. The South had none. Not to mention, South Vietnamese military inherited a mess left by the US military. The population was now very hostile to them. After 1973, the US failed to supply the South with the supplies and aides it had promised. Meanwhile, North Vietnam received increase supplies and aides from both China and the Soviet Union. You could fill in the outcome from here.