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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 main reason why the Southern states seceded was that they believed that Lincoln and Congress would not support their region's best interests. Therefore, the correct answer is option C.
