Close your eyes ...

Imagine yourself as an investor more than a century ago -- before the industrialization of the United States. Would you have bet your money on the growth potential of our nation? Knowing the outcome a hundred years later, you wouldn't hesitate to answer.

We can't rewind to the past
Unfortunately for our generation, those days are long gone on domestic soil. The opportunity for high-flying GDP growth and rapid infrastructure development is in the past.

Gross domestic product growth in the United States has averaged just 3.3% annually for the past 25 years. It will struggle to reach even 1% this year, despite continuous technological advancement in the United States. And because many guru investors, including Warren Buffett, argue that GDP growth is a key ingredient to long-term market returns, the future doesn't look so bright for domestic-only investors.

But even if you weren't around for the roaring '20s, you didn't completely miss your chance for the exponential growth that infrastructure development can offer. While the U.S. can no longer capitalize on heavy infrastructure expansion for growth, beyond our borders lies a world full of nations -- exploding with growth -- that can.

A new investment frontier
China and India won't be running out of steam soon, but these countries are already emerging and are off to a great start. To capture the even more exciting early years of initial growth, you need to find economies that possess characteristics that point toward becoming the next emerging market.

While not as prominent as the BRIC foursome of Brazil, Russia, India, and China, investor buzz is starting to collect around tiny economies such as Vietnam, Indonesia, and Bulgaria. Dubbed the "Frontier Markets" by the Barra Index, these economies are just beginning their development stages; they hold less than 1% of the money invested in stock markets worldwide.

But that will all change soon. Goldman Sachs anticipates that Indonesia and Vietnam will be two of the 15 largest economies. And looking at the accomplishments of past emerging markets, the prospects are enticing. According to a recent Newsweek article, the current major emerging markets, including China and India, also held fewer than 1% of worldwide stock market money back in 1987. Today, that share has increased to 12%.

Sign me up
Unfortunately, gaining access to these markets isn't always that easy. While a handful of notable American depositary receipts (ADRs), such as Chile's LAN Airlines (NYSE:LFL), offer investors direct exposure to these frontier economies, there aren't many companies available for direct investment. But that doesn't mean your only option is to fall back on an ETF or closed-end fund.

The key is to search for strong global players that can capitalize on the growth in these countries by investing portions of their business there. This will provide exposure while minimizing some of the risk inherent in investing in frontier markets.

For example, Motorola (NYSE:MOT) is expanding its network in Vietnam with $28 million in new contracts. Alcoa (NYSE:AA) announced earlier this summer that it signed a cooperation agreement with the Vietnam National Coal-Mineral Industry Group to help develop the aluminum industry and perform due diligence on a potential acquisition in Vietnam. Citigroup's (NYSE:C) Private Bank is looking to set up an investment fund to capitalize on Vietnam's booming real estate market, particularly focusing on higher-end properties for the growing middle class.

In Bulgaria, major IT companies are flooding the country. Salaries are reportedly skyrocketing by the double digits for Bulgarian programmers as Hewlett-Packard (NYSE:HPQ), SAP (NYSE:SAP) and Dell (NASDAQ:DELL) expand their operations into a country full of savvy math and science graduates willing to work for a fraction of what employees earn in developed countries.

Although you probably associate Nigeria with scam emails, it's the largest oil producer in Africa. U.S. energy companies such as Chevron are so bullish on the country's prospects that, since 1999, the U.S. energy sector has invested nearly $11.2 billion there.

And it isn't just enormous companies that are optimistic. Fund managers are tapping into these countries for foreign portfolio exposure. According to Cliff Quisenberry, manager of the Eaton Vance Tax Managed Emerging Markets Fund, countries in the bottom 4% of the world capitalization universe returned roughly 18.1% annualized over the past decade, versus a 5.6% average return for developed markets.

Don't miss your chance this time
A recent U.N. conference had good reason to rank Vietnam as the sixth-most desirable place to invest. Simply put, frontier markets offer untapped potential to informed investors.

That's why our Motley Fool Global Gains analysts recently returned from some of these markets (Indonesia, Vietnam, and Singapore, as well as China). Gain access to their best findings, as well as a free trip report, with a free 30-day trial.

This article was originally published on May 24, 2008. It has been updated.

Kristin Graham , a contributing analyst for Global Gains, does not own shares in any of the companies mentioned in this article. LAN Airlines is an Income Investor selection. Dell is an Inside Value recommendation. The Fool has a disclosure policy.