Final answer:
The Ku Klux Klan was organized in Tennessee in 1866 to terrorize former slaves who voted and held political offices during Reconstruction.
Step-by-step explanation:
The organization that was organized in Tennessee in 1866 to terrorize former slaves who voted and held political offices during Reconstruction was the Ku Klux Klan. The Klan started as an oath-bound fraternal order of Confederate veterans and eventually evolved into a vigilante terrorist group that used acts of intimidation and violence to suppress African Americans and white supporters of Reconstruction.