Preservation of slavery was a major factor in the secession of the first 7 states. A common defense against a pending Northern invasion was certainly the primary reason for secession of the last 4 states. States Rights, a socio- economic rift that had started decades earlier, and slavery were all integral----all necessary for a secession of the Southern states. Just as free black people were the primary reason for the antebellum Black Codes in five Northern states.