This article examines the ideological features and main activities of the First Ku Klux Klan in 1865‒1867. Having emerged as a reaction to the ongoing policy of the North, the Clan has shown numerical growth and an increase in the ranks of its supporters since its foundation. This was mainly due to the policy of radical Republicans in the South, which limited the rights of supporters of the former Confederacy. The study is based on the use of a variety of sources, including biographies of Clan leaders. The organization, which has rapidly increased in size and geography, has transformed from a political club with secret signs and symbols into a serious threat to the stability and well-being of its political opponents. The period under review is characterized by the transformation of the Clan and the associated clan movement into a militarized secret terrorist organization that supported conservative southern politicians and became the mainstay of local racists.