I think thats generally the reason people include international funds in their portfolio, specifically because they can behave differently than US stocks, and over a longer time line they have provided similar returns, so the combination provides the same high return with lower volatility. True, they've been on the losing end the last 10 yrs, but thats really not that long, and to some, thats something in their favor currently. Personally, I ask myself the question, is there a convincing reason why international companies should provide a worse return than domestic companies in the future? I am no expert, but I have no suitable answer for that question, so I include them.