Most nations have had their prime and period.
What's important is now though, and not what happened back then.
Even if you were a superpower back then, but cannot keep up with the race of evolution/development today, chances are, that in the future you will become extinct or not have any chance at all to regain former glory/superiority.
As science is developing these days, there are less and less need for physical strength and imposing physiques, when you can do so much with artificial means (robots and whatnot) these days and even moreso in the future.