The only country capable of international intervention (the US) had already done about as much as it could to prolong the life of the Khmer Republic. It was already apparent that the Khmer Republic was doomed by 1972, and public opinion in the US was against prolonging the war or continuing the carpet-bombing and aid which had kept the communists at bay between 1970 and 1973. After April 1975, initial reports of excesses by the Pol Pot regime were disbelieved by leftist intellectuals such as Chomsky. There simply wasn't any will on the part of any foreign powers to intervene in what was by then seen as the lost cause of communist SE-Asia. Cold war politics and the warming of relations between China and the US led to the continued support for Pol Pot's faction after the Vietnamese invasion. Human rights took a back seat to realpolitik.