Relax, said the nightman
We are programmed to receive
You can check out any time you like
But you can never leave
These pages have considered various topics related to secession, including its use as a means for coping with oppressive government and the various secession proposals by states, including Northern ones, prior to the Civil War.
This article, however, raises several interesting points about secession and slavery in mid 1800s America that have not been well considered on these pages.
One point is that the abolitionist movement included a strong disunionist thread. Per fugitive slave laws that were reinforced by the Dred Scott decision in the late 1850s, federal marshals were empowered to hunt down escaped slaves that had made their way to Northern states. That federal agents could enter a state that did not permit slavery, and capture and return escaped slaves to states that permitted slavery led to several nullification and secession proposals by Northern states.
Another point is that both Southern state decisions to secede and Northern decisions not to secede were costly miscalculations w.r.t. the slavery institution. The South's decision to secede was a miscalculation because the legal system of the US favored slavery at the time. Although many Southern states were concerned about future additions of more 'free soil' states that would have tilted balance of power away from Southern states, this was not a near-term proposition.
Constitutionally, an amendment was required to emancipate slaves in Southern states. To obtain 3/4 states approval, 26 additional states would have to be admitted and vote in unison with the 19 non-slave states to amend the Constitution to prohibit slavery. Because this was unlikely in the near term, Southern states were foolish to secede if their intent was to maintain the institution of slavery. Of course, slavery was not the only motive behind the South's secession.
On the other hand, for any abolitionist who could do the constitutional math, then the best prospects for near term change in the slavery status quo was Northern secession. Secession would have removed Northern state obligations to permit fugitive slave hunts by federal agents. Such states would have become more attractive destinations for people wishing to escape slavery--thereby increasing rate of escape of Southern slaves to the North. As rate of escape increased, viability of the slavery institution decreased.
Furthermore, secession by Northern states would have voided the Constitution in those states. Anti-slavery states could have written a new constitution where equal treatment under the law would not be compromised for personal gain.
An interesting question to ponder is why, once Southern states actually seceded, didn't Northern states immediately move to amend the Constitution to eliminate the 3/5 and fugitive slave clauses and get their houses in order? Border states would become even greater magnets for slaves escaping from the South which would have put added stress on the slavery institution in the South.
People in the North could have followed that up with a voluntary (not forced) trade embargo with the South. Southern states, being heavily dependent on Northern industrial goods, could hardly have lasted long on their own. Chances were good that many Southern states would have sought to resume a voluntary union with the Northern states for economic reasons. Those returning states would have faced a legal system that had been constitutionally revised to uphold the rights of all.
Secession by either the North or South opened a door for peaceful resolution to the slavery issue.