Yes, we allowed atrocities, if you mean that we didn't send in American troops.
Don't keep me guessing, what's your point?
Couldn't we also say that atrocities were committed in Iraq and Vietnam (napalm, anyone?) and Cambodia? There are reasons that Kissinger is considered a war criminal in some circles, ditto Cheney.
What about the Uyghurs, Myanmar, Sudan, Ethiopia? More than one head of state is responsible for the sorry state of the world.