There's the Geneva Convention. Not all countries have signed on, and the countries that have don't necessarily follow them all the time or when they think no o

There's the Geneva Convention. Not all countries have signed on, and the countries that have don't necessarily follow them all the time or when they think no one is looking, but that doesn't mean that there aren't mostly-agreed-on standards for what is or is not a war crime. If universal adherence were a necessary characteristic of ethical standards, we wouldn't have many that pass that test.