Wall Street Journal columnist Jason Zweig writes that while data shows how the S&P 500 has outperformed international stocks for years, the numbers can “play tricks on you. It still makes sense to add international stocks to a U.S. portfolio, probably more so than ever.”

Zweig notes that while the numbers show that the U.S. market has dominated over the long run, it’s only because stocks have done so well in the recent past. “Lofted by a strong currency and trillions of dollars of fiscal and monetary stimulus, U.S. stocks rose so swiftly out of the financial crisis that they left the rest of the world behind. That spectacular recovery has obscured the historical record.”

In the 1970s and the 2000s, according to Zweig, the U.S. was among the worst-performing stock markets worldwide. Over the decade through December 2007, he adds, U.S. stocks underperformed the rest of the world by an average of 3.1 percentage points (annualized). “No one can say when that might happen again,” he writes. “Chances are it will.”

Toby Thompson, a multi-asset portfolio manager at T. Rowe Price Group Inc. in Baltimore, notes that the rest of the world’s markets are less dominated (on average) by technology stocks than the U.S. and more focused on “cheaper industrial and financial stocks,” adding that the prices of such stocks outside our borders are “a lot more compelling.” Regarding the strategy of globalizing a portfolio by simply holding multinational U.S. companies (e.g. Coca-Cola or Intel Corp.), Thompson explains that such companies tend to hedge their foreign currency exposure, so whatever the U.S. markets and economy are doing “tend to overwhelm whatever benefits the companies get from being global.” Therefore, although the businesses are multinational, the shares behave like U.S. stocks.