But it is still having an effect.

Yes, there have been wars since.

But Bush is having to justify his invasion plans to the rest of the world.

The UN won't stop any country from doing whatever it wants.

But community opinion does have some bearing.

While the US can veto any resolution it does not like, that does not mean it can pass any resolution it wants.

Diplomacy instead of war.

Even if it has to start only between the nations who can veto your resolution.