Answer:
D. Democrats enacted laws that made segregation legal
Explanation:
Started from the 1870s after the Reconstruction, it was the Southern, white dominated, Democratic Redeemer governments that enacted Jim Crow laws, which officially enforce racial segregation of the Black people from the white population across the South.
The Jim Corw's law that was passed prevents the African Americans from voting and segregated schools, restaurants, and public accommodation.
Hence, After Reconstruction ended, the factor that allowed for segregation to spread throughout the South is that; Democrats enacted laws that made segregation legal