A simple yes or no, to satisfy my personal curiousity. Nation X has been killing its citizens by the thousand, stuffing them into mass graves. The estimated death toll is 500,000, and looks like it will reach a million within ten years. Nation Y wishes to invade. For the purposes of this question, let's assume Nation Y's motives are entirely to do with saving lives, and there is nothing else to be gained from invading. Heck, maybe it will even be a financial loss for all involved. Either way, Nation Y wants to invade, destroy the government of Nation X, and prevent further murders. However, Nation Y predicts that the invasion will cost the lives of ten thousand innocent citizens of Nation X, plus or minus 25%. Is it right for Nation Y to invade Nation X?