Foreign stocks have had a rough go of it compared with U.S. stocks over the past decade. That might be about to change. Stocks in foreign developed markets as well as emerging markets have greatly underperformed U.S. shares for years, pushing U.S. stock valuations far above foreign valuations. Even last year, when stocks were strong world-wide, the average U.S.-stock mutual fund or exchange-traded fund rose 28%, outpacing the average international-stock fund’s 23% advance, according to Refinitiv Lipper data. This year, U.S.-stock...