This stuff has been going on for decades. You didn't hear about it cause the Internet wasn't a thing and we were less connected. Even like a strike between a labor union and employers the amount of violence would blow your mind. Explosions, shots fired, etc.
I'm guessing the guys who attacked the police headquarters are white and are trying to start a race war or something. Black people don't use bombs as much, they will tell you it's because they're not as crazy as whites.