Complex sentence: Governor "Pitchfork Ben Tillman", a Populist, led the effort to disenfranchise the blacks and poor whites, although he controlled Democratic state politics from the 1890s to 1910 with a base among poor white farmers.
Split into simpler sentences: Governor "Pitchfork Ben Tillman", a Populist, had led the disfranchisement effort. He controlled Democratic state politics from the 1890s to 1910 with a base among poor white farmers.