There are many categories that the USA leads the world in. Obesity for one.
One item is invention. Inventing new concepts, whether for peacetime or wartime or anything inbetween, the USA still probably leads in this category. Case in point, the United States invented Stealth Technology that the world is now chasing. TONS more examples, but you get the idea.
The USA is probably going to be surpassed in economic output. Standard of living, the USA is already behind several nations. Can anyone thing of a plan with which to surpass the USA in invention and new ideas? Even nations like Japan and Germany borrow heavily from US inventions. The USA is just an excellent climate for making inverntors.