Here is a GDP evaluation from year 1:
This shows that demography drives GDP when everything is equal, all agrarian economies, all industrial, or now, all post-industrial. China and India have been the two highest GDP from the very beginning as they were the most populous. CHanges began in the xix century, when Britain and the Netherlands were the first to start the industrial revolution, soon followed by other Europeans. Also colonization played an essential role in creating imbalances for the profit of the European powers. Then, comes WWII, with the US supremacy.
What is happening now, is just a return to the natural economic world balance, given by demography. The current crisis is just the beginning of our (The Western world) fall. A shrinking economy, a drop in positions in word leadership, a loss of influence on world politics will not happen painlessly.
This is just the beginning.