Earlier this year, the Department of Justice blocked Penguin Random House, owned by the German media giant Bertelsmann, from acquiring Simon & Schuster. The big five publishers—HarperCollins, Penguin Random House, Hachette, Macmillan, and Simon & Schuster—already control about 80 percent of the book market. The literary class was relieved.Less than a year later, the private-equity firm Kohlberg Kravis Roberts announced that it would buy Simon & Schuster. Because the firm doesn’t already own a competing publisher, the deal is unlikely to trigger another antitrust probe.