What about the following ideas from Jacob Hornberger and Tom Woods? Of all the articles I have read about the Civil War, these are my two favorites.
Hornberger: “Moreover, there was another way to bring an end to slavery without all the massive death and destruction that Lincoln’s war entailed. The North could have acceded to the secession and then declared itself to be a sanctuary for runaway slaves.
What about the Fugitive Slave Act, which required Northern states to return slaves to their owners? It would have been gone. Remember: with secession, there would now be two separate and independent countries — the United States of America and the Confederate States of America. There would be nothing the Confederacy could do to force the North to return runaway slaves.
That would have undoubtedly broken the back of the slave system in the South. After all, slavery was a dying institution anyway, not only in a moral sense but also in an efficiency sense. Operations based on slavery could not compete against enterprises based on consensual, paid employees. It was just a matter of time before the entire system collapsed. A sanctuary system in the North would have accelerated its demise.”
Woods: “It is not plausible to suggest that slavery could have lasted much longer, even in an independent South. With slavery being abolished everywhere, the Confederacy would have been an international pariah, and it is unreasonable to suppose that it could have long withstood the inevitable and overwhelming international moral pressure to which their isolated position would have exposed them. And according to Jeffrey Rogers Hummel, whose study of the war has been hailed by mainstream historians, ‘The fact that emancipation overwhelmed such entrenched plantation economies as Cuba and Brazil suggests that slavery was politically moribund anyway.’
Slavery was doomed politically even if Lincoln had permitted the small Gulf Coast Confederacy to depart in peace. The Republican-controlled Congress would have been able to work toward emancipation within the border states, where slavery was already declining. In due course the Radicals could have repealed the Fugitive Slave Law of 1850. With chattels fleeing across the border and raising slavery’s enforcement costs, the peculiar institution’s destruction within an independent cotton South was inevitable.
This latter point recalls the earlier suggestion of abolitionist William Lloyd Garrison: a division of the Union would have hastened the end of slavery. It so happens that, as Hummel observes, this is precisely how slavery was destroyed in Brazil. The institution essentially collapsed there after being abolished in the Brazilian state of Ceará in 1884. A hastily passed fugitive slave law was largely ignored, the value of slaves fell dramatically, and within four years the Brazilian government had acknowledged the reality of the situation by enacting immediate and uncompensated emancipation.”