The correct answer is C) Immigration.
The American Civil War consisted of fighting between the Union and the Confederacy. After the election of 1860, seven different states seceded from the Union because they were afraid that Lincoln would expand the power of the federal government (therefor giving states less rights) and that he would try to abolish slavery. Abolishing slavery would ruin the Southern economy, as this area relied heavily on slave labor to produce goods such as cotton.