Todd Jensen emailed that he and his colleagues have posted what they believe to be the 10 Worst Riots in American History. Interesting list, but off the top of my head I can think of two more notorious ones: the Chicago Race Riots of 1919 resulting from conflicts among immigrants, and the World War I veterans' riots in 1932. In the Great Depression, hungry veterans marched on Washington, and were blasted with water hoses by President Hoover's minions.
Riots are generally sparked by desperate and angry people. Yet they often produce a backlash that is counter-productive to the goals of the demonstrators. The riots of the 1960s and early 1970s helped create the reactionary third party candidacy of Alabama Governor George W. Wallace who abandoned the Democratic Party to call for "law'n'order." The ultimate beneficiary of his apostasy was Republican President Richard Nixon.