Of course it was a secondary consideration.
“Lincoln went to war to defend the nation and ended up saving the slaves; the south went to war to defend slavery and ended up losing everything”.
At the time of the war every northern state had either freed their slave populations or had enacted a pathway to emancipation. So while there were still pockets of slavery in northern states the conclusion to that chapter was defined.
Lincoln knew that no “executive order” could end the practice of slavery. That would take a constitutional amendment. In the meanwhile he also knew that he could take a decisive step toward abolishing the practice and knock the rebels back on their heels in the process. The symbolism was sublime and the act did literally free blacks in the south, even in areas outside his immediate control.
It seems to me with all the pressure to add a free and slave state at the same time it’s hard go imagine that the issue of slavery was not uppermost in the issues addressing the nation.
I think seven states succeeded from the time Lincoln won the election until his innagural. Lincoln talked a lot about saving the union, but this is a cart before the horse issue. The south was succeeding to maintain their states right to have slavery, not because Lincoln was dedicated to preserve the union.
The South didn’t go to war to defend slavery. In his First Inaugural Address Lincoln supported the Corwin Amendment, which had passed the Congress AFTER 7 Southern states had left:
Lincoln stated:
“I understand a proposed amendment to the Constitution has
passed Congress, to the effect that the Federal Government
shall never interfere with the domestic institutions of the States, including that of persons held to service. Holding such a provision to now be implied constitutional law, I have no objection to its being made express and irrevocable.”
Lincoln and his administration, then, were quite willing to make the Union “safe” for slavery forever. If slavery had been the issue for the South, the seven states would have returned because they had been given a complete, crushing win on the issue.
Slavery was a cause of tension among the states, but the South’s concerns over the tariff (which had a long history as a source of strife and had lead SC years earlier to contemplate nullification or leaving the Union (Jackson threatened to invade)and federal corporate welfare for Northern Industry, as well as other federalism concerns, were the main drivers. There was no “cause”, however. Federalism, tariffs, slavery, and other issues were all bound together in a way that led the vast majority of Southerners to want independence.