Why the US lost in Vietnam

The Vietnam War, America's longest war, had ended up in failure for the US. At that time, and until today, the US was the strongest nation on the planet and Vietnam was one of the poorest and a primary industrial country, where peasantry was in majority. The war, more officially, began from 1964 and ended in 1972 and the main reasons for losing the war was underestimation of VC, Ho Chin Minh Trail, Vietnamese people, protests back in the US, efficiency of US troops, cultural differences, and US casualties.
The US has underestimated Vietcong and the NLF. They had supply from the USSR and Ch…