A Direct Cause of the Civil War Was the Attempt

A direct cause of the Civil War was the attempt to expand slavery into the western United States. Why did slave owners want to expand into the West?

A) The practice of planting only one crop tended to deplete the soil in the South.
B) The governments of some southern states began to outlaw slavery.
C) There were more slaves in the West than in the South.
D) Northerners were moving into the South, so the slaveowners had to move West.