In 2012, the U.S. government sued to block the world’s biggest beer maker, Anheuser-Busch InBev, from buying Mexico’s Grupo Modelo (which manufactures Corona and other beers) for $20 billion (Brent Kendall and Valerie Bauerlein, “U.S. Sues to Block Big Beer Merger,” Wall Street Journal, January 31, 2013). Anheuser-Busch InBev had 39% of the U.S. beer market, MillerCoors had 26%, and Grupo Modelo had 7%. When the suit was announced, both firms’ stock prices dropped sharply. Why?