Here are some various opinion on why (and whether) the US lost the war in Vietnam:
1. We lost the war because of America's foreign policy. It was to stop the spread of Communism, not do be rid of it. They would have been able to destroy Communism in many different times like the Korean War. Lyndon B. Johnson didn't want to be rid of Communism because that would make us sound like an Empire again like with the Philipines in the Spanish American War and right now in Iraq. We lost the war because of forfeit. Johnson said no to being rid of Communism like Truman said no to McArthur in the Korean War. We had an open door and a 100% chance of destroying Communism, but we didn't have the permission.
2. The United States did lose the Vietnam War. They were not able to overthrow communism which was their aim as presented to the public. Pulling out is a loose term for admitting defeat. The VC were vastly superior in their tactics and numbers. They had cause to be at war, many of the GI's believed Americans did not. There is no denying it, America lost the Vietnam War.
3. The United States pulled out of the Vietnam war. We did not lose it. Technically, we were not at war, we were advisors but the Congressional approval to fight in Vietnam was not given. If anyone lost it was the people of Laos and Cambodia who came under Communist rule after the war.
4. Lack of interest. No one was that interested in stopping the Communists aggression in the Far East. And as the war went on the cost in blood & treasure seemed extreme and fruitless. Didn't lose,just withdrew. We could have won a better deal on tungsten,rubber,chromium,China containment,security. You can't please everyone, but it helps. Kept going that long with the support of China, Russia & the U.S. allies. + the draft was ended c. 1970 that made the war more tolerable; then war crimes & napalm tuned off the rest.
5. The only reason the US lost was because we withdrew from there. The US won every battle but the Vietnamese were willing to sacrifice many more lives than the US.
6. They lost because the politicians did not let the military do their job. They made decisions that should have been made by generals. Politicians should not make tactical decisions.
7. The people of South Vietnam did not want to fight that war and the U.S.A. didn't want to fight that whole war for them without much help from them.
8. Some of these answers are so deluded. America lost the war in Vietnam for various reasons. A few of the reasons are listed below, providing some idea of what happened in Vietnam even if it is a shallow overview: The US troops completely underestimated the VC,who were skilled jungle fighters, and also had mass peasant support. The American tactic 'search and destroy' increased VC support. As one soldier said "If they weren't VC before we got there, they sure as hell were by the time we left"
9. I don't think that some of these answers were from deluded people. There are several reasons as to why we didn't win the war. There is truth in most of the answers given. True, we alienated a lot of the Vietnamese because of atrocities but we weren't the ones that were going into villages and disembowling the leaders or raping their women or taking a machette to babies. The VC did that. Yes, there were some unfortunate incidents like Me Lai but that is one incident compared to thousands of atrocities that the enemy soldiers did. Second, the US military was extremely handicapped by both the war planners and the US media. In order to make bombing runs we had to contact a war planner back in the States to get permission to make a bombing run. Then we were not allowed to bomb anything close to a civilian area no matter how strategically important it was because we were humane enough to want to not injure the North Vietnamese civilians. Were the North Vietnamese that concerned about not hurting anyone? Absolutely not. They had no compassion whatsoever. They placed no value whatsoever on human life. Sometimes when they would attack to try to overrun our bases the first wave of soldiers' purpose was to die on top the barbed wire perimeter so that their fellow comrades could walk over their bodies and enter the compound. They were so fanatical they would fight till the last man was dead. As far as the Vietcong being a skilled fighting force that is a crock. They were poor, not very well trained, deluded people who were virtually eliminated after they made a massive attempt in 1968 to take over the country. They were temporary successful but once the US military got to work, end of story. We literally slaughtered them. Then there is the US media who were probably the biggest traitors to the US cause and have a lot of our young men and womens blood on their hands. It seems so strange that when we would announce to the media that we were going to make a bombing run to a certain location that when the bombers would get there that the enemy soldiers would announce to the media that we were going to make a bombing run to a certain location that when the bombers would get there that the enemy soldiers would be gone. And the media also helped to stir up the anti-war movement back home thus being an ally of our own enemy. Right before we decided to pull out of the war we had the North close to surrendering. But you won't hear that from the news media. We had killed close to a million enemy soldiers.
10. The US did not lose the war. The Paris accords were signed and all but 1,500 U.S troops were still in Vietnam when Saigon fell. The reason Saigon fell was also the fact that the South Vietnamese Army was not willing to stand and fight for their own country.
11. America didn't lose the war in terms of politics. The Paris Agreement states that the US won as troops were still in Vietnam at the time. In terms of casualties and deaths, however, I think it was pretty equal going.