The reason we have rules of war is so we can react with some degree of international cohesion when they are broken. It's a deterrent for the little guys: follow the rules or the wrath of god will come down on you. Supporting you will be poison and in all likelihood you have damned your cause.
Honestly it seems like a win-win for humanity. The premise is, of course, that larger nations have the incentive and wherewithal to avoid total war. This cornerstone becomes the foundation to pull other nations without the maturity or international presence up to these standards.
Obviously if any nation, alliance, or cohesive group is adequately threatened they will never pull total war off the table. Rules of war / engagement help keep it off the table in areas where armed conflict is a threat with a much higher frequency than the first world. Frankly, autonomy and sovereignty have not existed since economies globalized, and that's also probably a good thing. We're moving towards a humane and cohesive world, but we're not there yet, and constraining war is a triage until we are.
A world without war is not a pipe dream, and, I would argue, an inevitability as countermeasures and technology continue growing in destructive power and ease of acquisition. However, looking at the state of the first world, much less its trading partners and the rest of humanity, we all have a lot of rapid cultural development and normalization to go through before we're ready.
The Internet will be the herald of all of this. So, tech world, keep up the good work.