China has over a billion people, mostly ethnically unified, intelligent, hard-working, criminally non-inclined. America has 300 million people who are, in aggregate, a continental multi-national empire, as was the Austria-Hungarian Empire or the USSR.
The only difference between the US and these empires of yesteryear is that we didn't invade new lands to obtain a diverse population. The diverse populations invaded us.
there was an article posted yesterday that said diversity is more important than ability. So ethnically unified might be disadvantage compared to diverse population of US.
Give it ten years, and we're #2.