You may be right, but who else would do it? I feel like Russia would be invading the entire EU, and China would invade Taiwan if they thought they could get away with it.
Countries should be left to handle their own affairs; that's the responsibility that is inherent to sovereignty. The premise of a global hegemon who babysits the world and enforces the rules (dictated by themselves and their allies of course) is an anachronistic leftover from the age of imperialism. If the rest of the world wants America to play world police (and for the most part, I don't believe they do) let them pay the American public for this service.
In a world where we have 9 nuclear powers, I struggle to see how your system would keep them in check; nuclear fallout effects all of humanity and quite literally could make the planet inhabitable.
I bring this up because any system that replaces the current world order needs to be able to keep these nuclear powers in check.
