There are no such things as "war crimes". It's fucking WAR. You're killing people on the other side, which is already a crime!!!
I guess the people that believe in "war crimes" have never heard the quote "all is fair in love and war."
This is not how works the international laws. Giving the massacre of WW2 mmost of the countries signed international conventions on war. We can't strictily forbid war, because in order to stop a war you have to go to war, what you are supposed to prevent, so you can't just say war is a crime, it always depends of the context. But internationnal laws put the framework of what actions are allowed even it is individual crimes it is not a "war crime".
And their is a concrete list of war crimes, even if you are on war, some limits you can't cross in order to prevent the war from escalating to the worst methods.
- Those war crimes includes attacking civilians intentionnaly
- Destroying buildings that are not millitary (especially hospitals, shelters, religious building etc..)
- Attacking humanitarian missions
- Killing soliders who surrendered
- Deporting people from their land
- Torture, rape slavery and other inhuman or degrading treatments
- Using weapons that are strictly forbidden (toxic gas, acids and chemical weapons)
- Starving civilians
- Using childs on the conflict
And some of those when reaching extreme gravity become crimes against humanity that doesn't just incriminate the states but incriminates all people who participate on those, like genocides.