The great historian Arnold Toynbee explained the precarious position of the "universal state". In his historical theory the "universal state" comes into being just as a civilization begins a headlong descent into disintegration. In our situation, American cultural and military dominance came into being as a result of the disintegration of western / european culture.
A universal state is not geographically universal (i.e. its borders do not encompass the whole world). It is called a universal state, because it is dominated by the notion that no external force in the whole world can threaten it.
The Roman Empire believed this. In fact, the politicians of the day argued vehemently that the Goths, Visagoth, Saxons, Teutons and Vandals posed no threat to the might of Rome. However history tells us that those Germanic tribes defeated Rome. They lived in fringe communities, and while they copied the culture of the universal state, they nevertheless sought its destruction.
Another aspect of the universal state is the civil religion that it develops to butress its divine claim to power (e.g. last week Dubya ripped a few lines from the Gospel according to St. John the Divine when he refered to the United States of America - and not God in Christ - as the "light that shines in the darkness...") Rome had Caesar worship. We have manifest destiny.
We are in a precarious position, because universal states normally, but not always, mark the end of a civilization. The arrogance of the universal state doesn't take interior and exterior threats seriously and I believe your observations illustrate this.
Our planned incursion into Iraq presents us with many diplomatic and military problems.
Our inclination to rule by force is also problematic. No nation has ever been able to rule by force for an extended period of time.
Certainly the United Nations is dominated by third world nations who seek to hamstring the first world. They are, after all, the fringe societies that seek to imitate us simultaneously seeking our destruction. You know... American pop-music, Levi's and an AK! However, that doesn't mean that we shouldn't be engaged with them. In fact, that is even more of a reason to enter into diplomatic relations with them.
Perhaps if the Caesar had opened trading relations the Celtic tribes instead of seeking military superiority, Hadrian's wall would have never been built.
In short, I'm afraid that we'll be dumb enough to be lured into entering yet another unwinnable David and Goliath type conflict.