What group besides african americans suffered from ku klux klan attacks apex?

The Ku Klux Klan (KKK) was originated in 1866 by young men in Pulaski, Tennessee, as a social club. This movement initiated as group of pranksters, that soon turned into intimidation of blacks and  white Republicans.

During the postwar years, a new revival of the KKK. Now they were opposed to the Reconstruction in the post-Civil War South. They were against not only African Americans but also Roman Catholics, Jews, and immigrants. After the WWI we faced another revival in the movement. This time following the nativist idea of the prejudice caused by "foreigners". The new Klan was restricted to militant white Protestants born in the US. And in its final conception, they were anti-Negro, anti-alien, anti-red, anti-Catholic, anti-Jew, anti-Darwin, anti-Modern, anti-Liberal, Fundamentalist, vastly Moral, militantly Protestant.