 Secret vigilante and insurgent groups such as the Ku Klux Klan (KKK) instigated extrajudicial assaults and killings in order to keep whites in power and discourage freedmen from voting, working and getting educated.They also sometimes attacked Northerners, teachers, and agents of the Freedmen's Bureau.A study of the period from 1868 to 1871 estimates that the KKK was involved in more than 400 lynchings.