The U.S. third-quarter real GDP growth numbers came out this morning and, well, they're abysmal. The domestic economy grew just 1.6%. That's the lowest rate since 2003, markedly lower than the 5.6% growth we posted in the first quarter, and nearly 50% less than the 3% growth we've come to expect.

So what the heck happened?

The bull hits the fan
The housing slump was to blame for much of the slowdown, and economists seem optimistic heading into the fourth quarter. So hopefully this isn't a sign of things to come. That said, isn't it a sign of lowered expectations that we'll be ecstatic if the country rebounds and posts 2.5% GDP growth in the fourth quarter?

From 1950 to 1990, real GDP grew at 3.5% in real terms or 7.7% nominally. And from 1990 to 2000, our country posted 3.3% real and 5.4% nominal GDP growth.

Yet since 2000, we seem stuck. Real GDP has grown just 2.4% since the turn of the century. And now we're at 1.6%.

Don't panic
Some of this is to be expected. After all, we're an enormous and mature economy. Take the percentages out of the equation and the United States is a more than $12-trillion-per-year enterprise. That's nearly 30% of the global output.

And just as large, mature companies such as General Electric (NYSE:GE), Microsoft (NASDAQ:MSFT), and Wal-Mart (NYSE:WMT) have taught investors about the inverse relationship between growth and size, that's a lesson all Americans are learning now as well.

It's the law of diminishing returns -- depressing as that may be.

All is not lost
Here's the good news: The U.S. economy does not exist in a vacuum. As investors, we are not condemned to suffer from a domestic economic slowdown. Just as most large American companies, including Yum! Brands (NYSE:YUM), Ford (NYSE:F), IAC/InterActiveCorp (NASDAQ:IACI), and Wrigley (NYSE:WWY), are either already investing heavily in growth abroad or thinking strategically about how to do so successfully, you should be doing the same.

Seriously, if you're not hot on the trail of the world's best stocks, you may be condemning your portfolio to a decade of underperformance -- or more.

Get out your passport
There are many countries that are currently growing their GDP's by more than 3%, 4%, and even 5% annually. That list includes China, Estonia, India, Pakistan, Qatar, South Africa, and Thailand.

So -- and you had to know this was coming -- do you own shares of any companies headquartered in these countries?

If not, you should, because if you don't, the global economy may leave you in its dust. That's why we recently introduced our Motley Fool Global Gains investing service. Led by senior analyst Bill Mann, the service aims to help seasoned investors round out their portfolios with smart foreign picks that will not only benefit from but spearhead global economic. If that sounds like a proposition worth investigating, sign up for free 30-day access to Global Gains today. Check out the team's inaugural picks and country-specific research on us.

Tim Hanson does not own shares of any company mentioned in this article. Microsoft and Wal-Mart are Inside Value recommendations. Wrigley is an Income Investor pick. The Motley Fool's disclosure policy keeps us all on our toes.