Why did we leave it up to the Vietnamese to liberate Cambodia from the Khmer Rouge?

Because, thanks to Richard Nixon and "Dr." Henry Kissinger, I would ume that the Cambodians didn't really want our "help". The Khmer Rouge came about as a direct result of the illegal US bombing of their countryside, causing a civil war that culminated in the Khmer Rouge's holocaust in Cambodia. Therefore, because Cambodia's prior uninvolvement in the wider Vietnam war didn't seem to work for them, "anybody but the USA" was most likely the deciding factor. The tragedy of Cambodia is a major reason why we should leave well enough alone, becuase we don't know what we are doing. Look up the book called "Sideshow" It explains what happened there in the 1970's.