One of the first times we let them rewrite history.
After the war of 1812 the north pushed for tarriffs. They said it was to stop the south trading with our enemies, but the reality is they wanted to drive down the price of cotton and other goods farmed in the south for their factories.
The tariffs were HATED in SC they called the first one the tariff of abomination, and when jackson only slightly reduced them in 1832 they called a statewide convention and declared them null and void in SC. Congress passed a force bill that authorized Jackson to us the military against SC and war was saved by a compromise at the last second.
In the next 3 decades the government worked together on compromises. Till the north gained enough control to pump up their factories again. Nothing changed in SC. The second the pro tariff party won power the people of SC were like "fuck it, I'm out." The slave/free state expansion stuff only mattered because slave states would likely be agricultural and anti tariff and free states would likely be industrial and pro tariff.
It is an absolute hard fact that the south would have traded slavery for lower tarriffs.
The other hard truth is that the after the southern states left Congress a government made up of 100% northern states attempted to stave off war by passing a constitutional amendment permanently enshrining slavery, and lincoln sent letters agreeing to sign it.
If the south wanted to keep slavery they just needed to come back and ratify the amendment and if the north wanted to end it they just needed to trade for lower tsriffs.
The civil war was not about slavery, it was about money.
Taxes. It started because of fucking taxes. The slave bit was a gambit by the north to try and create an insurgency. Lincoln only "freed" the slaves in the States who seceded. Fact.
"If I could save the Union without freeing any slave, I would do it; If I could save it by freeing all the slaves, I would do it; and if I could do it by freeing some and leaving others alone, I would also do that." - Abraham Lincoln
Pragmatic fellow, it does sound like slavery wasn't the top priority.
One interpretation is that he knew announcing emancipation, news of that would reach the slaves in the South and they would rise up against the Confederate soldiers' families back home. A pretty shrewd move, knowing that no soldier would remain in the field and leave his family defenseless.