Let's begin this debate with a trivia question, OK?

According to Capital IQ, there are 39 stocks with market caps in excess of $10 billion that have doubled in price over the last year. How many of the top 10 were based in the U.S.?:

  • All of them; multibaggers are All-American, dude;
  • None of them; the domestic stock market is for losers;
  • More than half; USA! USA! USA!; or
  • Less than half; Gooooooooaaaaaaaaal!

Believe it or not, the answer is less than half. But the total is much worse than less than half. It's actually -- get this -- two: agriculture conglomerate Archer Daniels Midland (NYSE:ADM) and oilfield services firm Schlumberger (NYSE:SLB).

Not made in America
The top five includes a pretty startling array of North and South American firms. Schlumberger is the lone American entrant. (Yet even that's not a solid claim; Schlumberger was founded in France in 1926, according to Wikipedia.) Here is a list of the other four:

  • Petroleo Brasileiro (NYSE:PBR), a Brazilian oil producer;
  • America Movil SA de CV (NYSE:AMX), a Mexican wireless services operator;
  • Suncor Energy (NYSE:SU), a Canadian energy company known for pulling oil from sand; and
  • Canadian Natural Resources (NYSE:CNQ), another Canadian energy firm and one of the stocks the bargain hunters at Motley Fool Inside Valuesingled out last year in a reader contest. Nice pick.

Look, I understand this list is arbitrary. It's just as likely that American stocks will dominate the next top 10 list. You know what? I don't care. And neither should you. Eliminating a potential market-beating investment on the basis of an address is as small-f foolish as it gets.

No borders
Besides, for all the good news about the U.S. economy, there are others that are performing even better. Take Brazil, for example. It's the largest economy in Latin America, newly energy-independent, and racking up huge trade surpluses. Indeed, economists project a $40 billion surplus for 2006 because of increased demand for the country's rich commodities reserves.

Now, contrast that to the U.S., which has a $202 billion trade deficit with just China. And recent talks between Chinese President Hu Jintao and President George W. Bush seem to have yielded no tangible results on this issue. Might that affect stocks long-term? I've no idea, but it's hard to imagine it will help much.

Invest abroad without leaving home
Here's another myth: International investing is a lot riskier than other types of stock investing. Sorry, Fool, but that just isn't true. There are literally hundreds of international stocks you can buy as American Depositary Receipts. Here's a definition, pulled straight from our Foolish glossary:

A receipt for the shares of a foreign-based company held by a U.S. bank that entitles the shareholder to all dividends and capital gains of the underlying stock. ADRs trade similar to stocks on U.S. exchanges, and provide a way for Americans to invest in foreign-based companies by buying their shares in the U.S. instead of through an overseas exchange.

In other words, ADRs provide investors with the benefits of foreign diversification and the protections afforded by American securities laws. That's right, ADR issuers are required to file documents with the Securities and Exchange Commission, like any other American public company.

Practicing what I preach
I firmly believe Fools should have a diversified portfolio that contains both American and foreign stocks. Or, in lieu of stocks, well-diversified foreign stock funds. And I'm putting my money where my mouth is: I own the Julius Baer International Equity fund, which has made me a pretty penny since I bought it three years ago. I also hold positions in Nokia (NYSE:NOK) and two small Canadian firms: One is a uranium speculator and the other a mattress retailer that is to Canada what Select Comfort is to the U.S. All four holdings have easily trounced the S&P 500 in the time that I've held them.

The Foolish bottom line
Beating the S&P 500 consistently is really hard. Doing so requires a certain arrogance and temperament, as former Fool contributor Whitney Tilson once wrote. I'm not as eloquent; I simply think you need to zig when others zag, and vice versa.

There are numerous ways to do this, of course. One is to buy stocks on sale. Another is to buy into seemingly improbable growth stories. And, of course, there's international investing. All are great tools, and can be equally powerful when it comes to seeking stock market riches. Ignore them -- any of them -- at your portfolio's peril.

Get 14 other reasons to take your portfolio on a market-beating trip around the globe by picking up The Motley Fool's inaugural international stock report, Around the World in 80 Minutes . Or, subscribe to any of our investing newsletters and get the report free. All you have to lose is the prospect of richer returns.

Think you're done with the Duel? You're not! Go back and read the other three arguments, and then vote for a winner .

Fool contributor Tim Beyers last used his passport on a recent trip to Canada. He highly recommends Montreal. Tim owns shares of the Julius Baer International Equity fund and Nokia. You can find out what else is in his portfolio by checking Tim's Fool profile . Select Comfort is a Motley Fool Hidden Gems recommendation. The Motley Fool has an ironcladdisclosure policy.