Don’t know that I’d draw the line so vividly at the Great Wars. The US made major shows of force against Spain, Mexico and others as early as the 1810s. By the mid-1800s, there was no real question as to which countries could effect their will in the world.
Had it not been for the American Civil War, the US would have established itself as an unquestioned superpower even earlier. Heck, Lincoln threatened the UK with invasion to keep them from meddling on the South’s behalf during the Civil War. How’d a second-rate nation in a brutal civil war tell off a supposed superpower Empire?
By the 1860s, the North alone had a standing army of 600,000. The entire British Empire had just 130,000 – of which 30,000 were bogged down in India, and the rest spread thinly around the globe, often ill-equipped and really more occupying security for the colony companies than true soldiers.
I suppose you could make the argument that the British colonial armies (who were even worse-equipped and poorly-trained than their regular counterparts) would boost the British number a few tens of thousands, but then you’d have to consider that the entire mobilization forces for the Union (again, alone) were well over 1 million.
The US was undoubtedly a superpower by the end of the 18th Century. A neophyte, but a superpower nonetheless.
. You sound almost like a Marxist 