An interesting table in The Economist compared the market capitalizations of stock markets in developing nations. The first surprise is that the top seven stock markets are so close to each other in size. The next observation is that stock market capitalization has less to do with the GDP of the country than one would expect. China, which has the largest economy by far among countries on this list, has a smaller market cap than India or Russia. That Hong Kong and Taiwan approach China in size despite vastly smaller populations makes China look even more surprising. The large and wealthy diasporas of India and Han Chinese of Taiwan and Hong Kong are also a reason why these countries have market caps larger than their GDPs would suggest.
In any event, these numbers are dwarfed by the United States, which has a total stock market capitalization of $20 Trillion, or 30 times greater than that of South Korea, India, or China. One company, General Electric, if placed on this list, would be between Taiwan and Mexico to take 9th place. And the US market cap grows at 8% a year (without assuming acceleration), which would bring it to $130 Trillion by 2030. If China or India want to match the US market cap in size by 2030, that means they have to grow at 25% a year for the next 24 years straight.
This tells you how far any other country is from surpassing the US as an economic superpower. This will be worth visiting again when one of the countries above crosses $5 Trillion.