UN was created to stop wars like the WW1 and WW2 happening again, but while one could argue it was successful in that (I believe other factors have come into play, mostly increased standard of living), it has anything but stopped separatist conflicts.
To me the UN sounds like the right place to extend the goal to stop wars even further: it's where countries come together and agree on shared values, goals and rules.
I don't care if it's UN or anything else, if we are worrying about corruption, we'd need to design for that too because it is inevitable in any organization.
Let’s take two examples. What’s goin on in Myanmar atm, they are supposed to sucede? From who? Who will tax them? Another example, let’s say hypothetically Texas decides the US is too liberal and sucedes. The liberal US will tax it at the liberal, starting a war. The US was even founded because of extreme taxation, which led to a war. Taxes = war. Give people away to defend themselves, then you’ll stop wars.