The greatest world powers militarily in 1930 were the British empire, and the American empire.

That hasn't changed since, although the Soviet Union gave us a good run for the money during the Cold War.

And China has been amassing a shitload of weaponry, technology, and training of a huge fighting force, and hasn't spent any of it's payload to date, except in some skirmishes here and there. Which is why the US doesn't want to test their military might.