Apparently, in 2014, China overtook the United States as the world's largest economy (edit: As measured by PPP adjusted GDP. Sometime relatively soon, we can expect the US economy to be smaller than China by other accepted measures as well). Considering it is only the third largest country in the world, seems like it's had (edit: or will soon have had) a good run. But has the US been just a historical flash in the pan?
Well first i'd like to point out that the post on r/worldnews which you are referencing is misleading. The U.S. is still the world's largest economy. China now has the largest Purchasing Power Parity.
This by no means says that China has a larger economy than the U.S. In terms of GDP (which is the accepted common form of measurement for economies) the U.S. still vastly overshadows China. It even says so at the end of the article.
So in essence OP's question doesn't work out since the basis of it is false.
This graph from the Economist shows historical share of world GDP. The US emerged as the world's largest economy about 120 years ago (perhaps a bit more). For most of recored history economic demoninance was shared by India and China.
Maddison, quoted on Wikipedia gives more detailed numbers. His numbers show that India was the dominant economy in 1 CE, and had a run of about 1500 years before being overtaken by China. Exact numbers and dates probably aren't too reliable, but we can safely say that India's dominance was at least ten times as long the US's. For the next few hundred years, India and China traded the top spot. It should be noted that, according to these numbers, the UK (the dominant Western power before the U.S.) was not able to overtake China before it was itself overtaken by the U.S.
If current trends continue, it does indeed seem that Western economic domination, made possible by their early adoption of industrialization, will be a "flash in the pan" amongst the greater story of Chinese/Indian dominance.
It's also worth noting "GDP" is a modern construct, created by Americans in the 1930's
Comparing the economies of modern countries, with our massive amounts of trans-oceanic trade, or even with industrial economies of the 1800's, with ancient economies is fairly useless.
essentially pre industrial revolution GDP meant ag output and china won because it's the place that could control the most land. a similar thing explains india's dominance (though india was much more fractured). Hence if you want to go into ancient history what you are really asking is why did China, Persia, etc. have long lasting huge empires since without an industrial or deeply trade based economy (spain colonizing based on gold) places with a natural ag advantage would clean the us' clock. China beats the us because 1. it developed an early state under the qin, 2. scale helped fir massive irrigation projects (wittfolgel's thesis in oriental despotism) and 3. wars and undefended frontiers spurred larger empires (why europe's mountains seas and rivers are important: hard to build an empire)
fukuyama had a neat book in 2011 about this sort of thing and part 2 is released this year.
