https://www.battlefields.org/learn/articles/reasons-secession
Slavery
1) Each declaration makes the defense of slavery a clear objective.
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Mississippi: Our position is thoroughly identified with the institution of slavery— the greatest material interest of the world. Its labor supplies the product which constitutes by far the largest and most important portions of commerce of the earth… These products have become necessities of the world, and a blow at slavery is a blow at commerce and civilization. That blow has been long aimed at the institution, and was at the point of reaching its consummation. There was no choice left us but submission to the mandates of abolition, or a dissolution of the Union, whose principles had been subverted to work out our ruin.
Texas: The servitude of the African race, as existing in these States, is mutually beneficial to both bond and free, and is abundantly authorized and justified by the experience of mankind, and the revealed will of the Almighty Creator, as recognized by all Christian nations.
South Carolina: Those [Union] States have assumed the right of deciding upon the propriety of our domestic institutions; and have denied the rights of property established in fifteen of the States and recognized by the Constitution; they have denounced as sinful the institution of slavery; they have permitted open establishment among them of societies, whose avowed object is to disturb the peace and to eloign the property of the citizens of other States.
Georgia: That reason was [the North’s] fixed purpose to limit, restrain, and finally abolish slavery in the States where it exists. The South with great unanimity declared her purpose to resist the principle of prohibition to the last extremity.
2) Some states argue that slavery should be expanded.
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3) Abolitionism is attacked as a method of inciting violent uprisings.
4) Mississippi and Georgia point out that slavery accounts for a huge portion of the Southern economy.
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States’ Rights
1) The states argue that the Union is a compact, one that can be annulled if the states are not satisfied with what they receive in return from other states and/or from the federal government.
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2) The states argue that the North’s reluctance to enforce the Fugitive Slave Act of 1850 (mandating that fugitive slaves be returned to the South) means that the compact is no longer satisfactory.
Other Grievances
1) All of the states negatively mention Abraham Lincoln’s election and his suspected abolitionist leanings.
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These may be in the written reasons for secession, but they are not necessarily reasons why the men fought and died. To know that, you would have to ask them, or their heirs to whom they shared the knowledge.
Indeed, most of the men who actually fought and died could neither read nor write.
There were 11 states in the CSA, yet somehow you people can only find 3 or 4 of these secession documents that mention slavery as an issue. You completely ignore those ones that don't.
How about Virginia's secession document? Want to quote that one?
Because it doesn't show what you wish to believe, people generally won't talk about Virginia (The most important state in the CSA) and why they left the Union.
Also, if you want to see a different take on the slavery angle, Paul Craig Roberts has you covered.
https://www.paulcraigroberts.org/2018/11/13/a-civil-war-lesson-for-the-uneducated/