1945 is probably a good counterexample. If Hitler had kept his regime and genocide locally and not invaded neighbours, there would be no WW2, everybody would let him do that.
Just like in Cambodia, or Rwanda, or North Korea, or many, many other examples - as a rule, the world does not intervene with violent regime change just because a regime is abusing their people. Like, nobody in power batted an eye when Saddam gassed Kurds in his territory, intervention happened only when he invaded Kuwait. I'm not even sure if I have seen a single exception in 20th-21st century history; it feels like humanitarian aspects have been only used as a pretext or justification if there were other politic/economic reasons that mattered more than that.
