Warren Buffett, once the world's richest man, once joked that his enormous success owed completely to his good fortune 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 controlled the two top spots for worldwide wealth. But they've both been usurped now by the planet's new richest person, and he's not from the U.S.

In 2007, that crown now belongs to Mexican business tycoon Carlos Slim, who's worth roughly $59 billion. Like Buffett, whose wealth is directly related to the performance of Berkshire Hathaway's (NYSE:BRK-A) (NYSE:BRK-B) stock price, Carlos Slim's riches are tied to the value of his major holdings. His 30% stake in Latin American wireless provider America Movil (NYSE:AMX) alone is worth some $31 billion. Shares in America Movil have more than quintupled since 2004, and the stock's strong performance in 2007 is one the primary reasons for Slim's rise to the top.

Testing: One billion, two billion...
At any moment, the stock price changes of Microsoft (NASDAQ:MSFT), Berkshire, or America Movil will determine who's No. 1, 2, or 3. Buffett, Gates, or Slim could care less, and neither do I. While I strongly believe that the United States will maintain its economic might, I also believe that the 21st century will belong 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 by holdings operating outside the U.S., only reinforces my opinions about the investment opportunities available abroad.

Emerging economies display some similiarities 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 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 other 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%-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 after the Buffett pop. Today, the company trades around $145 a share or so.

The U.S is still home to the strongest and safest equity market -- recent credit turmoil notwithstanding. In addition, the vast growth potential in emerging markets has driven up foreign stocks' prices across the board, reducing your likelihood of finding a good value there. China's political climate seems to favor free-market capitalism, but until it completely embraces democracy, the U.S. should still remain your first source for bargain-hunting.

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 you 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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Fool contributor Sham Gad is the managing partner of the Gad Partners Fund, a value-centric private investment partnership operating in very similar fashion to the 1950s Buffett Partnership. He has no positions in the companies mentioned. The Fool has a simple disclosure policy.