system
Given the following post, respond as if you're commenting on Reddit:
human
War isn't a game. So why are there rules for war? What incentives does a nation have for adhering to them?
gpt
The idea that war isn't a game is very new. Up until World War I, it didn't really occur to anyone that wars weren't a valid diplomatic tool; declaring war on someone was just a strong diplomatic statement, like cutting off trade or recalling your ambassador. The point of diplomacy is (broadly) to get other countries to respect you, and following the rules of war made you seem more respectable.

In modern times, when every war has at least one side seeking to eliminate the other side completely, you're completely right that rules of war don't really make sense. This is why they're regularly ignored.