Jay Winik's new book, a bestseller, is April 1865: The Month That Saved America (HarperCollins). He writes that April 1865 is a month that could have unraveled the American nation. Instead it saved it. During that month the war ended with Lee surrender, Lincoln was assassinated, and the rebuilding of the nation began. Winik is a senior scholar at the University of Maryland School of Public Affairs and a regular contributor to the Wall Street Journal.