Torture, rape, mass executions of civilians and prisoners of war, the usual.

The atomic bombings are the most prominent examples, but there were also the horrible. 'conventional' bombings of German cities like Dresden.

And fire bombing of most of Japan, knowing very well that they would torch hundred of thousands of civilians including women and children.

And the ongoing killing of prisoners who surrendered (a US army speciality in the Pacific, no prisoners, just kill them all)