Britain fell due to the necessity of containing a neighbouring state which have bigger population, better productivity, and the advantage of not having an empire abroad of a continent.
At the end, the Brits fell after pummeling Germany two times.
Both haven't recovered fully today.
So this historical analogue doesn't really speak well to both US and China in the next, say, 3 generations. Wonder who would be the US in this situation though.
Did you know that the GDP of Africa is two trillion dollars (PPP)? So Africa has surpassed Canada, right?
What matters is GDP/capita, not total output in a nation of 1.4 Billion people. You can easily get "first place" by redrawing boundaries around a bunch of poor and middle income nations. That redraw doesn't make anyone better off.