@themanj The "allied" powers also carried out war crimes, so it does not matter if you follow the rules of war, only if you end up winning or not. Historians and the powers that be overlooked/ignored/encouraged allied war crimes because they "won".
Black water didn't really get punished, and the same can be said of many groups of insurgents in the middle east.
So people DON'T usually follow the rules of war, because history shows that they don't.
It makes people fight more viciously though, in the hopes that they win. Yes, the losers will be punished more harshly for any "war crimes" they committed, but the winner's war crimes will often be completely ignored.
Look now at the USA elections, many rules and common practices were broken, the left in some of the most blatant foul practices we've seen in over a hundred years have broken rules all in order to win their little cultural war. They will only be punished if the other side doesn't also too decide to fight dirty.
If a civil war broke out because of this, again I highly doubt people would follow the rules of war. Not just because they want to viciously win, but because they simply are ignorant to any actual rules of war.
If the side that is cheating, then proceeds to tell others they aren't allowed to do something because it is against the rules, the sheer hypocrisy alone would probably lead to some of the most dirty horrendous war crimes we've yet to see in our modern era.
So to reiterate, people don't usually follow the rules of war, they simply just ignore the crimes of the winner and do what they can to further punish the loser.