Really bad analogy, (Brussels : Europe is far more like Washington DC : USA than UN : World. - though that is also off).
And I think you misstate the "UN is irrelevant" crowd a bit. What a lot of people think is:
1) The UN can achieve a lot if the USA pitches in. If the USA doesn't… then the UN is hamstrung. But the USA could also do aid/peacekeeping on its own. When the UN projects power or rushes emergency disaster relief to somewhere it is often due to the USA (who could have done it anyway).
2) The UN is a mix of democracies, dictatorships and theocracys. A coalition that only consists of democracies may, while limited in number relative to the whole of the UN, have far more moral authority and better judgment.
My view on UN authorizations for war:
1) As a "moral" authority: laughable.
2) As a "legal" authority: perhaps it is technically but I have a minor worry - These kind of legal precedents against starting wars may deter western democracies from starting wars but they are unlikely to deter an aggressive dictator (what will deter dictators from aggression is what they think is the likelyhood of the USA intervening to stop them. Note: not the UN, but the USA… even if the USA were to deploy under UN banners it still requires a US President to be willing to put US Forces there and without that the UN would generally be useless, see Kuwait, Korea etc)
Most points I don't take issue with and I was stabbing in the dark a bit on the brussels thing thinking more of the EU functions operating from there... I was in haste...
But my broader point remains. The idea that the UN is "irrelevant" in international relations is just plain silly. The fact is that there are thousands and thousands of different things going on under UN auspices. The "UN is irrelevant crowd" doesn't recognize this, because to them the UN is a body that:
A) Sometimes the US has to cajole to get what it wants
B) Sometimes the US has to bypass when it can't get what it wants
C) An organization that can't get action on crises like Darfur and Rwanda
D) (optional) a venue for antisemitism
A and B are a product of the fact the most print in the US about the UN is generated when the US is in the process of preparing for war - and more fundamentally - an American-centric worldview.
C) ignores the fact that collective action is, well,
collective and that the failures of action in places like Darfur or Rwanda stem mostly from nation states within the UN slowing action due to national interests like resource acquisition or geopolitics or simple unwillingness to sacrifice blood and treasure. (Darfur: China, Russia, Rwanda: France, America) Instead of looking past the UN and to the mechanics of what results in action, they stop short.
D) is a fair enough point, but again, rather more due to the fact that certain nation-states have taken an antagonistic position vis à vis Israel, and use their presence in certain organs of the UN to express those views. Again: the "UN is irrelevant crowd" stops short of analyzing just how these statements and resolutions come into being. Its the nation-states within the UN, not "the UN" that is doing this.
And besides A, B, C, D and there are many, many functions outside of the headline-grabbing items I've listed above. Things that are
very much relevant to the world like serving as a venue for complex inter-state negotiations on finance, regulation, labelling, transportation, hazardous and illegal goods, and territorial claims in the ocean and on land. It does humanitarian missions, disease and environmental work, development in third world nations, peacekeeping and observing of "hot" zones, research on the environment and the sociological impediments to growth. Really, the list goes on and on. Many millions around the world have felt the impacts of these things, which means that no matter what some cowboys in the heartland say, the UN is
relevant to the world at large.