U.S. corporate margins came under pressure in 2015 and early 2016 largely as a result of sliding oil prices, weak industrial activity and a strong dollar. But more recently, energy prices have stabilized and the other headwinds have dissipated. As a result, S&P 500 earnings growth has accelerated over the past three quarters. While valuations look stretched in many areas of the U.S. equity markets, a continued improvement in earnings growth could ease valuations and bolster equity price levels. And although it may not be the time to add additional exposure to the U.S., it should remain a core foundation for portfolios.