We know that United Nations was established in order to maintain peace worldwide? But there have been many wars between countries in history even after its establishment... So what exactly was UN doing at that time, what was its role? Regardless mentioning about various tense areas even in current era.. l
I see the point in critics you state, there were numerous wars which couldn't be prevented by UN. The purpose of UN is to prevent wars, genocides and to give a forum where all the members can try to solve their problems diplomatically.
The criticism isn't without base, previously the League of Nations failed for same reasons, by lack of power preventing the second world war, since influental nations left the LN. UN is different in a way that all great powers have veto power, so for a major nation the UN won't turn into a seriously burdening organization. In exchange of course it suffers efficiency decrease.
I would like to point out some cases when UN had it's purpose even if the efficiency might be a subject of debate.
- There was no "World War Three". I am sure most of us are happy with this fact.
- There were numerous examples when Nikita Sergeyevich Khruschev held speech in UN, once he banged his shoes in UN, I wouldn't say this is the nicest example of a diplomatic move, but it is obvious if he has the same amount of anger nearby the nuke launcher pad, things could go way worse. Fun fact: the photo of the incident is fake.
- Kosovo independence didn't emerge to a long lasting war, which is more or less depended on UN peacekeepers.
- Northern-Southern Cyprus conflict didn't turn into war.
- Stabilization of Haiti since 1993
We can say: there is a purpose for UN, but it is obvious, it is not functioning with 100% success rate, and it will never do.
The purpose of the UN is to have an open diplomatic channel between superpowers while letting the rest of the world feel important. This is why everything that has any impact goes through the security council, and all the permanent members get veto privileges. There were other stated goals about preventing genocides and war, but the UN has been pretty bad at both of those.