My reading of the U.S. Civil War is that tensions began when the federal government wanted to accelerate to the development of high tech industries in the northern states by increasing tariffs on manufactured imports. This hit the southern states hard because their agricultural economies require a consumption of manufactured goods to produce raw material; equipment bought from Britain would be used to make cotton which is shipped back to Britain to be manufactured and exported again. This dynamic explains why the British elite were in favor of the south (possibly hoping they would regress the entirety of the U.S. to an agricultural economy), while the British public were more often sympathetic towards the north. This action, among other things the federal government did, resembled the old English tyranny that everyone's parents and their parents' parents had fought and died to be rid of.
Slave-plantations are unsustainable. A workforce must be free before it can be trained to farm in such a way that does not rapidly deplete the land; this is one fact which contributed to the idea of white supremacy, as free workers were white, and free workers were taught more skills. With the rapid expansion of U.S. territory this would not become a problem in any single man's lifetime. I believe that those slave owning people who backed secession may have seen slavery driving the U.S. expansion, rather than the other way around, but that's just an opinion.
Anyway, coming back to emancipation, the Lincoln administration had a much clearer view of the relationship between capitalism and slavery since they were outside of the southern thought bubble. Plus anyone could see the potential in having former-slave armies: radicalized fighters with unlimited morale. "Freeing the slaves" is always a good idea when one is at war with slave owners.
Lincoln is one of the greatest presidents my country has ever had but in my view, the Civil War had almost nothing to do with asserting the equality of all people. When viewing it on paper it seems to me to have been about solidifying the authority of the federal government, as well as industrializing the U.S. economy to replace and eventually compete with foreign manufacturing.
Also, the U.S. is not a new kind of country. There were already several confederations of independent nations, living in the area when the Europeans arrived and began colonizing. I will concede that having a central government which can create and apply policy to all members of the confederation was "new" it was not "radically new" as it was only a remix of other, well-established models of government.