Why did the U.S. military intervene so massively in Vietnam in the 1960s?

The US was trying to help South Vietnam stay independent and repel North Vietnamese aggression. The only way the US could have propped up South Vietnam--it seemed in the 1960s--was to commit huge numbers of US soldiers.

The north vietnamese were supported by china and russia and it was the cold war so it just kind of happened. Had President Kennedy not been killed it may have gone differently as he was a proponent of special forces and had actual war time experience.....but we'll never know.

Terrified of communism, god knows why. How many thousands of miles is Vietnam from the USA?

Humans come from apes and as you should know. Apes fight for territory and domince. When you ignore all the political propaganda. You will discover that Humans are the same as apes. It's just on a larger scale.

The US wanted to suppress the spreading of Communism.

They trick by the French.