Inquisitor makes an important point: the illusion of a single world power makes it easy for other powers to evade responsibility.

One of THE dumbest things that I ever saw happen in international politics was the US telling "Old Europe" that it would attack Iraq no matter what they did or said. It made the decision for "Old Europe" trivial: why join in when the bad guy will go down anyway, and you can keep your powder dry (plus score points for resisting the war). "Old Europe" couldn't lose. It was so stunningly stupid.