The UN is not the reason for the delay in WWIII. Mutually assured destruction is the reason for that. The US and Russia conducted proxy wars for decades in spite of the existence of the UN.
Not true at all, world war is not synonymous with nucleat wat between US and Russia. Regional conflicts grow and draw in super power allies, before you know it you are fighting proxy wars and those proxy wars grow to actual battles. If and when nuclear powers feel their existence is in danger, they will use nuclear force.
Mutually assured destruction sounds nice in movies but in reality, it stopped the mighty japanese empire. Some look at nukes as a way to sacrifice millions to save billions. Some think even a nuke power like the US will not continue to escalate after a nuclear war because of political red tape or MAD,the US or Russia for examples might surrender and accept loss instead of riskiny a global nuclear war.
Sure, regional wars can grow into world wars. WWI was precisely that. However, the dynamics of war entirely changed after nuclear proliferation. There have already been dozens of not more than 100 regional proxy wars since WWII and none of them have triggered a true world war. So the UN was not effective at preventing regional war (which as you said can escalate to world war) but it is effective at preventing world war? I don't see it. I see individual nations acting in their own perceived best interests. I see US military dominance as this century's "Pax Britannica" (https://en.m.wikipedia.org/wiki/Pax_Britannica). But as the US's economy shrinks relative to global GDP and China's expands this peace will come under tremendous stress. I'm not convinced the dysfunctional UN will be the world's savior.
The UN facilitates diplomacy, instead of NATO deciding to do something about russia, they have a security council vote and with diplomacy form blocs of nations on each side of a conflict. Before the UN,an alliance like NATO will do something about russia and just drag in others. Not just the great war, but WW2 is a good example, diplomacy with italy and japan would have prevent or deescalate many of their aggressions, but at the same time response against the axist could have been global, imagine not waiting for an axis invasion but sending troops as part of a coalition force before they advance to you, problem was there was no place where nations could agree on a response.
If China starts invading asia for example, the UN can be used to sanction or even coordinate a resistance effort both diplomatic and kinetic before it gets out of control.
> WW2 is a good example, diplomacy with italy and japan would have prevent or deescalate many of their aggressions
How that could possible work?
UN talks to Italy and Japan saying: hey guys, we know you already killed a lot of people (especially you Japan, Nanjing Massacre), and we know you are Germany allies, but please, do nothing while we crush the Germany, and then we will liberate all the territories you have already acquired, but you just deescalate your aggression.
What would be the reason for Italy and Japan to listen the "UN"?
Oh, BTW, League of Nations existed prior to WW2, and Germany, Italy and Japan were it's members.
> If China starts invading asia for example, the UN can
China has veto. UN can't do anything against China.
Unless you are japanese that empire will not have treated you nicely. "The man in the high castle" shows how it might have been under japanese rule. No thanks.
Mutually assured destruction sounds nice in movies but in reality, it stopped the mighty japanese empire. Some look at nukes as a way to sacrifice millions to save billions. Some think even a nuke power like the US will not continue to escalate after a nuclear war because of political red tape or MAD,the US or Russia for examples might surrender and accept loss instead of riskiny a global nuclear war.