Investors have bet heavily on the U.S. economy. That's not a great idea

The world is growing nervous about U.S. assets and for good reason. Over the past 15 years, money from around the world has poured into U.S. stocks and U.S. bonds. That has led to a dramatically unbalanced situation in which nearly everyone everywhere has a financial stake, direct or indirect, in what happens in the United States, while the U.S. has only a passing interest in what happens elsewhere. Unless you're a market junkie, you may not realize how dramatic this shift has been. The numbers, though, tell a striking story, particularly in the case of U.S. stocks. Back in…