Complex sentence: In addition to resistance towards political change in the mid- 1900s, South Carolina's Democratic party prevented African Americans from voting in the primary election, which prevented African Americans from having a meaningful vote in the election.
Split into simpler sentences: In addition to resistance towards political change in the mid- 1900s, South Carolina's Democratic party also prevented African Americans from voting in the primary election. This prevented African Americans from having a meaningful vote in the election.