The Globe and Mail reports in its Wednesday edition that investors in U.S. stocks have enjoyed an extraordinary bull market for much of the past 15 years. Guest columnist Frederick Vittese writes that U.S. equities (S&P 500) have been the best-performing asset class since 2013, consistently outpacing the S&P/TSX Composite Index, international developed-market equities (MSCI EAFE Index) and Canadian long-term bonds. Between 2000 and 2012, however, the U.S. market never claimed the top spot, partially because returns are measured in Canadian dollars. International stocks have consistently underperformed. Over the past 25 years, even Canadian long-term bonds have held the top spot more often than the MSCI EAFE Index. It is noteworthy that when bonds were the top performer, stocks were not even close. While U.S. stocks have been dominant, their outperformance has come with rising risks. A significant portion of the gains has been driven by expanding price-to-earnings (P/E) ratios, making valuations increasingly stretched. If history is any guide, a reversion to the mean could hit U.S. stocks harder than other asset classes. Mr. Vittese recommends investors diversify across both asset classes and geographies.