Warren Buffett, who in early 2008 was the world's richest person, once joked that he owed his enormous success entirely to his good luck in being born in the United States at a time when the capital markets were ripe with opportunity. For more than a decade, Buffett and his friend Bill Gates had a lock on the two top spots for worldwide wealth.

Yet although the two again top the list in 2009, newcomers have recently climbed toward the top of the wealth list -- and many of those newcomers aren't from the U.S.

In 2007, the crown of world's richest man belonged to Mexican business tycoon Carlos Slim Helu. Like Buffett, whose wealth is directly related to the performance of Berkshire Hathaway's (NYSE:BRK-A) (NYSE:BRK-B) holdings, Slim's riches are tied to the value of his major holdings. His stake in Latin American wireless provider America Movil (NYSE:AMX) explains his rapid ascent: Shares in America Movil quintupled from 2004 to 2007 before dropping back in 2008.

Testing: 1 billion, 2 billion ...
For a while now, the stock price changes of Microsoft (NASDAQ:MSFT), Berkshire, or America Movil have determined who's Nos. 1, 2, or 3. Buffett, Gates, or Slim couldn't care less. While it's likely that the United States will maintain its role as an economic power, the 21st century may very well end up belonging to an emerging-market country. That powerhouse could be China, India, Brazil, or an African nation; the advantages of free-market capitalism have begun to attract people all over the world. Slim's rise to the top, propelled largely by holdings operating outside the U.S., only reinforces the fact that investment opportunities are available around the world.

Emerging economies display some similarities to the United States' conditions during the early part of the 20th century. Their populations are eager to become more educated, their governments are gradually adopting free-market-type economic policies, and their infrastructure direly needs improvement and expansion.

Thus, it's only prudent for intelligent investors to at least supplement their analysis of securities with businesses outside of the United States. You never know what you might uncover. At the very worst, you'll educate yourself further by understanding a foreign business. At the very best, you might find a buying opportunity, like Buffett did when he purchased shares of PetroChina (NYSE:PTR) in 2003.

A savvy international investment
When news of Buffett's buy first broke, PetroChina's shares shot up about 8%. Even after the "Buffett premium," China's largest oil explorer and refiner was selling for about $30 per American depositary receipt, or roughly $45 billion. At that price, the company was selling for about 25% of its large U.S. counterparts' asking price. Yet PetroChina was gushing cash and earning almost 80% of the profits that the U.S. oil titans were making. On top of that, the company was paying out 45% of its income in dividends each year, for a yield of 6% to 7%.

It didn't take a genius to realize that this was a fantastic business available for a good price. Yet part of the reason for the price discount relative to its American peers was that PetroChina was based in Communist China. Still, its valuation was extremely cheap even after the Buffett pop. By the time Buffett sold in October 2007, shares were trading around $150.

The U.S is still home to the strongest and safest equity market -- recent turmoil notwithstanding. Nothing shows that more than the dramatic drops in emerging-market stocks since last summer. Yet the vast potential in emerging markets has pushed prices of stocks like Petroleo Brasileiro (NYSE:PBR) and China Mobile (NYSE:CHL) back up, and investors are finding emerging markets attractive again. But you can also find good sources for bargain-hunting close to home.

At the end of the day, value investors simply focus on finding great businesses selling below their intrinsic value and offering a satisfactory margin of safety and return on capital. As long as you follow this philosophy completely, and maintain your discipline, the emerging markets are ripe with opportunities for the prudent investor. Just ask Carlos Slim.

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This article, written by Sham Gad, was originally published Aug. 27, 2007. It has been updated by Dan Caplinger, who owns shares of Berkshire Hathaway. The Fool owns shares of Berkshire Hathaway, which is also a Stock Advisor pick. Berkshire Hathaway and Microsoft are Inside Value selections. Petroleo Brasileiro is an Income Investor recommendation and America Movil is a Global Gains recommendation. Try any of our Foolish newsletters today, free for 30 days. The Fool has a simple disclosure policy.