By what arbitrary definition? There have been plenty of major empires with no realistic rival.

The term "Superpower" was first coined towards the end of the second world war, 1944. https://en.wikipedia.org/wiki/Superpower

That must have been a recent development,

No, I tried looking back to when the US might have topped the list of spending per student and couldn't find a single year. I was able to go as far back as 2005 when Norway was #1 and are still #2 today.

my point form the beginning was that we need to foster a healthy and balanced economy as well as deal with asymmetrical trade from China in order to maintain an economic, and by extension military, advantage

My point is that our economy has been stifled by terrible choices made by conservatives. Spending money at home, on infrastructure and education and healthcare would all be greater boons for the economy than starting wars of convenience.