What other groups besides the ku klux klan worked to reduce support for republicans in the south?

The White League and the Knights of the White Camellia also worked to reduce support for Republicans in the south.

The Knights of the White Camelia was an American political terrorist organization that operated in the southern United States in the 19th century, similar to and associated with the Ku Klux Klan, supporting white supremacy and opposing freedmen's rights. 
The White League, also known as the White Man's League, was an American white paramilitary organization started in 1874 to kick Republicans out of office and intimidate freedmen from voting and politically organizing.