In early April of 1968, a group of young people was sitting on the roof of a house near the line dividing Maryland from Washington, D.C., transfixed by what they were watching. It was the sight of the Nation's Capital burning down. That night, two of them tried to drive into the city, using one of its primary thoroughfares. They were stopped at a police barricade, and told that Washington was closed. The following day, after access to the city had...