Every superpower in history needed an enemy to finish it. We are the first to volunteer for the job.
Rome took centuries and a parade of invaders. Spain had the silver of two continents and still went bankrupt four times under one king, then spent 150 years losing wars. Britain walked into 1914 as the world's banker and out of 1945 as its debtor. The last payment on its war loan from the United States cleared in 2006. The Soviet Union rotted for decades before Afghanistan, cheap oil and an arms race it could not afford did the rest.