I believe that the U.N. was essentially dead the moment it was founded, at least in the sense of an organization with the moral authority to oversee relations between nations.

To allow Stalin's Soviet Union as one of the original security council members, a nation that had presided over the deliberate murders of nearly three times as many of its own citizens as Adolph Hitler's Germany.

For political reasons, maybe good ones at the time, this was overlooked, but the raw hypocrisy of the entire endeavor had to have been obvious to everyone, even if not at a conscious level.

Think of a neighborhood watch program that decides to include a local serial killer, or a police force that hires unreformed gang leaders.

Since then, the U.N. has been famous for treating murderous dictatorships pretty much the same as civilized nations, if not better, and the decay into the present bitter, anti-Western socialist club was probably inevitable.

NATO worked somewhat better, maybe because at bottom it was based on the foundation of a group of nations that valued (to at least some extent) individual rights, specifically opposed to nations that did not. Consistent, at least.