It’s meant to be a like minded agreement where if it ever came down to the countries going to war with each other, then the agreement is how war would be conducted. Take the Geneva Convention for example. If the US went to war with England for some reason, then the Geneva convention would be their ultimate code of conduct for the war to avoid unnecessary casualties, the management of pows and adequate reasons for ceasefires. It’s more just guidelines as they are rules. However if you’re a country outside of those agreements, then the guidelines don’t apply. It seems arbitrary, but the concept comes from a good place imo