In the first half of the 19th Century, the threat of secession became a tool to blackmail and hold hostage the Republic. The Southern states used that threat for half a century to not only veto the elimination of slavery, to not only veto any gradual reduction of slavery, but to veto any discussion of not expanding slavery into new territories as well as into existing free states. The confederate states seceeded because of the result of one presidential election, after they had already enjoyed a solid decade of support from favorable administrations and the shameful Tanney supreme court.
What could a Lincoln adminstration have actrually done if secession never happened? The most drastic thing he could have possibly gotten away with was to not enforce the fugitive laws, and then get booted out of office 4 years later. And possibly resist southern calls to invade Mexico, Cuba and Venezuela for the purpose of increasing the number of slave territories. And for that the confederate states claimed (with a straight face) that they were becoming slaves themselves. Gimme a break.
The catastrophe of the Civil War happened only because of an inability of both sides to compromise and reach a gradual solution. And the fact the the south decided that keeping (no, expanding) slavery was more important than both the future of the US and more important than a constitutional election put them much more in the wrong. Much more.
Most people are slaves to something these days and they don’t even know it.