>>520957478
The rules still apply, believe it or not.
The only difference is that nowadays there are some new laws about crimes against humanity. So killing an entire village of rebels is not kosher (if you end up losing, obviously).
One of Japan's defenses against the crimes in China was literally this. They claim that the "official" government of China (the Wang Jingwei regime) asked Japan for help to deal with those pesky warlords and communists :^)

Apparently there is an unwritten rule that it's okay to shoot people who don't have a flag.