system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What’s a “war crime”? I hear people throw this word around so much it’s confusing.
gpt
Many, many countries signed international agreements that define what is legal and what is not legal during a time of war. For instance, executing a prisoner of war who was not resisting or threatening his captor would be highly illegal. Targeting civilian buildings where a lot of civilians are is also illegal (like hospitals or schools). Killing civilians in general? Illegal. Wearing an enemy uniform or the symbols of an organization like the Red Cross, which is supposed to be a neutral symbol? Illegal. Attacking the Red Cross? Illegal.

It's pretty straightforward honestly. If you're attacking someone who's given up or who never even participated in the battle, you're probably doing something illegal.