They helped cause angry whites to form the Ku Klux Klan and other groups that terrorized blacks for years to come.

VOA: special.2010.02.04

By eighteen seventy-one, radical Republican congressmen were demanding a new law to destroy the Ku Klux Klan.

VOA: special.2010.02.18

Their campaigns often were led by members of the Ku Klux Klan.

VOA: special.2010.02.18

It was said that he carried a Ku Klux Klan card in his wallet.

ECONOMIST: Obituary

Years later, juries convicted three Ku Klux Klansmen and one suspected accomplice died without ever having been charged.

NPR: History Of US Bombings, Failed Attempts

In the same period violence from groups like the Ku Klux Klan and anti-abortion extremists have declined, Lewis said.

CNN: FBI, ATF address domestic terrorism