What caused conflict between the North and the South when Kansas and Nebraska prepared to become states?
A. Many Southerners believed that the new states would try to
secede.
B. Many Southerners argued that no new states should be added.
C. Many Northerners hoped the new states would ban slavery.
D. Many Northerners worried that Republicans would control the
states.

C, because if the South controlled the new states they would be slave states, and that was one of the reasons that led to the Civil War

Explanation:

the second significant cause of the great migration was the desire of black southerners to escape segregation, known euphemistically as jim crow. rural african american southerners believed that segregation - and racism and prejudice against blacks - was significantly less intense in the north.