Anon,
With all due respect, you do need to check your history, starting with Pol Pot. He was nothing to do with Vietnam; he was the leader of the communist faction (known as the "Khmer Rouge") in a neighbouring country, Cambodia. Early in 1975, the Khmer Rouge completed their overthrow of the pro-Western government of Marshal Lon Nol, when they captured the capital city, Phnom Penh.
Secondly, it was Richard Nixon who pulled US combat troops out of Vietnam. (Although, it must be said, after the Tet Offensive of February 1968, nobody had any further thoughts about winning the war - only about how America could best extricate itself from the debacle).
Nixon and his Secretary of State, Henry Kissinger, coined the term "Vietnamisation" of the war, in which - similar to Afghanistan - the local military were to progressively take over the fight. I can remember it like it was yesterday when the first US troop withdrawals took place during the latter part of 1969, and all the fanfare that was made of that event.
1969 was the first year of Nixon's presidency - and it was he that initiated the withdrawal of US combat troops, not LBJ.