Stephen Walt traces the beginning of the end to 1990 and the first Gulf war, which ushered in an era of American hubris about its ability to direct events in the Middle East to its and Israel’s liking.
It is noteworthy that he does not ask if the American empire is in a state of decline. He takes that as a given. The question is what has caused it.
It seems pretty obvious to me too that the US is heading for a major crash because of its unsustainable policies, a combination of oligarchical looting at home and disastrous wars overseas. What puzzles me is why more people, especially those in the upper levels of government, don’t see this and take the necessary steps to avert the catastrophe.