Protests that turn violent have been a constant throughout American history. Professor Ashley Howard explains their origins, and how new laws, policing methods, and social media have changed the way people demonstrate.   For More on this Topic: Check out her interview in The Chronicle of Higher Education and her piece in The Black Scholar. Read her two-page brief, How U.S. Urban Unrest in the 1960s Can Help Make Sense of Ferguson, Missouri, and Other Recent Protests.   Further Reading: How the Ferguson Commission Can Promote Healing and Reconciliation in Metropolitan Saint Louis, Eric Royer, University of Missouri-St. Louis How Social Movements are Using the Internet to Change Politics, Deana A. Rohlinger, Florida State University How Legacies of Urban Racial Segregation Shape Today's Controversies over Police Killings of Black People, Colin Gordon, University of Iowa