"As an amateur Civil War historian, I could name many different gangs/groups/rogue elements that spawned as a direct consequence of the conflict. The entire history of postbellum western settlement is littered with outlaw crazies and psychotic whackos who would murder a man for whistling off key."
This is true. James Gang, Billy the Kid, etc...However, the US Govt went after these thugs and eliminated them.
The difference between the Civil War ear and now is that these international "gangs" can blow up buildings and kill thousands of innocent people.