Why did the Southern states secede?

A. Northern congressmen voted to kick them out of the United States.

B. They disagreed with the pro-slavery stance of the North.

C. They believed that Lincoln and Congress would not support their region's best interests.

D. The North attacked them, starting the Civil War.

C. They believed that Lincoln and Congress would not support their region's best interests.

The Southern states seceded from the United States primarily because they believed that Lincoln and the Congress would not support their region's best interests. So the correct answer is C.