We have an encore of a discussion from May 11, 2020. Walter Johnson’s book reframes American history so that St. Louis sits at the center. No more looking at the nation as if it’s that New Yorker cartoon where everything important happened in New York City or Los Angeles, and the vast middle was mere flyover country. In Johnson’s telling, the St. Louis story is the American story — and it’s a messy, often ugly, one. The book is titled “The Broken Heart of America: St. Louis and the Violent History of the United States.”