The Klu Klux Klan

The Klu Klux Klan was a gang of violent white men who were pure racists.

The KKK terrorized people of the minority for no acceptable reason.
Klansmen would whip, murder, lynch, arson and rape innocent people.
These racists would wear white ghost costumes and abuse the minority in night time raids.

The KKK group was ruthless, they didn't care who they killed or how it affected people.
The KKK would venture to black schools and churches to bomb them.
This aggressive clan would kill black people and even children, simply because they were the minority.

Seeing how the KKK murdered the minority, you'd assume they were hard core killers. Although in reality, they never touched the white population.
For example, four Klansmen were arrested
in connection with the slaying of a civil-rights worker, a white woman, in 1964.
The murderous group believed in white supremacy therefore didn't ever hurt their own race. Although if you supported equal rights, they would see you as a target.

This proves that the KKK were one of the most serious, biggest racist group in history.