Alabama passed an ordinance stating their reasons for declaring secession:
Whereas, the election of Abraham Lincoln and Hannibal Hamlin to the officers of President and Vice-President of the United States of America by a sectional party avowedly hostile to the domestic institutions and to the peace and security of the people of the State of Alabama, preceded by many and dangerous infractions of the Constitution of the United States by many of the States and people of the Northern section, is a political wrong of so insulting and menacing a character as to justify the people of the State of Alabama in the adoption of prompt and decided measures for their future peace and security; Therefore,
Be it declared and ordained by the people of the State of Alabama in convention assembled, That the State of Alabama now withdraws, and is hereby withdrawn, from the Union known as “the United States of America,” and henceforth ceases to be one of said United States, and is, and of right ought to be, a sovereign and independent State.
The “domestic institutions” referred to slavery, of course. The ordinance goes on to note that “it is the desire and purpose of the people of Alabama to meet the slaveholding States of the South, who may approve such purpose, in order to frame a provisional as well as a permanent Government upon the principles of the Constitution of the United States…”