By Porter Stansberry in the S&A Digest:

I'd bet not one in 100 investors realizes last year was the worst year for the U.S. government bond market in more than three decades. The U.S. government bond market is the world's largest securities market. The question I've been wrestling with is: If this bear market in U.S. government debt continues (and there are very good reasons to suspect it will), what will investors buy when they sell U.S. government bonds?

They've got three choices... They could buy shorter-duration U.S. bills and notes. Plenty of evidence suggests lots of investors are doing that. Demand for short-term U.S. paper was so high in December some bills actually traded for a negative yield. Sooner or later though, the tiny yields (or even negative yields) and the weak U.S. dollar will force more investors to buy something else. That's why you see emerging-market bonds trading at record high levels. I bet emerging-market bonds continue to rally in 2010. And then, some wise investors who don't trust emerging-market bonds anymore than U.S. bonds will buy gold.

I bet these trends all continue for a long time: very low yields on U.S. government bills and notes, soaring emerging-market bond markets, and soaring gold prices. Of course, the surest bet of all is simply shorting the U.S. long bond. A bankrupt nation won't continue to pay less than 5% a year on fixed-rate, 30-year debt for long. You should also remember, the previous bull market in U.S. government bonds ran from 1981 until 2009 – 18 years. The bear market that follows is likely to be long and painful.

You might be wondering... What does the U.S. government bond market have to do with me? Maybe you only buy stocks. Maybe you'll never short the U.S. bond market or buy a Turkish government bond. No problem. But over the course of my career, I've learned you'll make your best long-term gains when you can identify an inevitable long-term trend and get in on it early. The biggest, most inevitable trend I see in all of the world's markets is in the U.S. government long bond. Understanding the ramifications of what's likely to be a decade or longer bear market is probably the most important investment question we face today.

Crux Note: The S&A Digest comes FREE with a subscription to Porter Stansberry's Investment Advisory. In just the past few years, Porter has shown readers how to make huge gains in gold stocks... how to profit from the demise of Freddie Mac, Fannie Mae, and General Motors... and the best ways to protect themselves from inflation and the unavoidable collapse of the dollar. You can learn more here.

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