The U.S and the dollar is the world's preferred reserve currency, and that position means that even if other countries have the money if the U.S economy were to tank, it would be disastrous for foreign countries as well. The book estimates 70% of China's 2.5 trillion reserves is invested in U.S debt. The U.S and China have a monetary bond and relation that Neil Ferguson calls, "Chimerica". China saves a significant portion of it's income, invests and exports more than they purchase and the U.S rarely saves, and instead runs a deficit through credit, purchases to full it's consuming and borrows money and purchases Chinese products. The book was very interesting to learn more about how global economics and finance interact with national policy.
What happens when other countries have the money, has been a question of mine ever since I started diving deeper into American history of the growth of wealth within this country. That wealth and power afford us a lot of things, but empires don't last forever, and slight balancing of power throughout the global economy could have big rippled effects here in the states. I was curious to see the economic and political, theoretical consequences of this question.