The most promising investment opportunities are increasingly found outside the United States, yet the vast majority of Americans place little stock in overseas markets.

That is a huge mistake, considering that China, India and other emerging markets promise superior growth, said Brent Ciliano, a portfolio strategist at Goldman Sachs Asset Management, who advises brokers and financial advisers on portfolio construction.

"The world is massively global. It follows your portfolio should be what the world is," he said.

The facts should speak for themselves, Ciliano said: 70 percent of small-cap stocks are outside the United States; two-thirds of REITs are overseas; about 55 percent of global equities are outside the United States.

Yet most U.S. investors have no more than 5 percent to 10 percent exposure to foreign markets, he said.

Thanks to the slowdown in developed markets, and the expansion of Asian markets, the rest of the world will represent a bigger and bigger share of the global marketplace.

Ciliano cited Ibbotson Associates research showing the U.S. share of the world's financial markets could shrink to 30 percent by 2030, down from about 45 percent at present. It was as high as 70 percent in the 1970s.

But Ciliano said the share held by other countries is increasing at a must faster clip now, which means the U.S. share could fall to 30 percent in just five years.

"International market capitalization relative to U.S. market capitalization is increasing faster than in the past," he said. "The rate of change is accelerating."

Foreign exposure is a key part of a "core and satellite" diversified investing strategy that Goldman has promoted since the late 1990s.

The strategy calls for surrounding a core portfolio with satellite assets — emerging market stocks and debt, U.S. and global REITs, commodities, high-yield debt and international small-cap stocks — as well as private equity, hedge funds and private real estate investments.

Ciliano says this approach has generated higher returns with less volatile swings than the typical "balanced" portfolio of U.S. stocks and bonds.

Ciliano said satellites and alternatives should comprise 15 percent to 20 percent of the overall portfolio. Some of Goldman's largest clients have as much as 49 percent invested in satellites and alternatives, he added.

The same portfolio services have been packaged for sale to smaller investors through investment advisers and brokers.

Goldman offers several Asset Allocation Portfolio funds, which make all these asset-allocation decisions, as well as funds that just invest in the seven satellite assets. Retail investors with as little as $1,000 can buy shares.

Another key component of the Goldman approach, hedge funds, also is more accessible to retail investors through vehicles that replicate hedge fund returns. Since its debut in June 2008, the Absolute Return Tracker Fund has attracted $730 million in assets.