Why did the USA lose the Vietnam War?

Why did the USA lose the Vietnam War?

The Americans did not lose purely for military reasons. There were other factors as well.

Write an explanation AND cite a source which shows the importance of the following six factors:

1. US military tactics in Vietnam
These military tactics caused many acts of inhumanity that shocked the American public. For example, the My Lai massacre. These caused the public to wonder what was actually happening in Vietnam, and if it was worth it. Also, the tactics were less effective in the jungle conditions in Vietnam, then that of the Vietcong, which were more suited for fighting in the confusing conditions of the dense jungle.
2. The unpopularity of the South Vietnamese regime
The South Vietnamese regime was very corrupt, and treated its people horribly, so much so that there were monks that burned themselves in protest to the intolerance of their religion. This caused the South Vietnamese at large to dislike their government, thus making them partial to the North. Furthermore, US public did not approve of the actions of the South Vietnamese government, lowering public opinion in support of the war.
3. The experience of the Viet Cong and the inexperience of the American soldiers
The soldiers in the Vietcong had to fight the entire war, making most, if not all of them veterans, and also had less of a chance to return home and influence public opinion. The US troops on the other hand cycled once a year, just as the troops were becoming accustomed to the war and also were able to come home and influence the public opinion again the war by sharing stories.
4. Domestic opposition to the war in the U.S.
The domestic opposition against the war in the US played a very large part in ending the war. First, there were extremely large antiwar protests, and second, most of the protesters were the young men who were scheduled to be drafted and go and fight in the war, making them unmotivated to fight, and want to fight the draft even harder. Finally, some refused to go to the war all together, and had to be arrested.
5. Chinese and Soviet support for the Viet Cong
The Chinese and Soviet support for the Vietcong gave them access to state of the art supplies from the Soviets, that while they were not as good as the American's, definitely helped them keep from being completely being overwhelmed by the American superior technology. As well as providing for the support of nuclear weapons support.
6. 'But did they really lose?' Summarize the argument put forward in Source 57, and your view on it.
The US did not actually loose the war for a few reasons. First the US left, the South Vietnamese lost afterwards, and the only reason the US left was public opinion, not military defeats. So, in essence I do agree with Source 57, but that does not mean agree with the war, just that there was no loose on the US's part. Also, it was not a war from the US's standpoint, just an 'armed conflict', so the US technically could not loose anyway.
Add other if you think there are factors you should consider.