There was the 1930 Sherman, TX race riot! It's not very widely known because there was a low number of casualties, but the Black part of town was destroyed and gov. Moody called for martial law at the urging of Texas Rangers (who were requested by the town to try and prevent a riot).

That's just one example that I know about because I studied it, but I know that aside from just good old-fashioned racism, one component of the aggression and violence is a sort of jealousy of the fact that most freedmans communities had a more or less self-sustaining economy (out of necessity and security in most cases). With the depression, EVERYONE was broke, so maybe seeing that their Black counterparts were suffering at the same level helped stem some of that racially motivated rage?