Of course it was democratic. It's easy to forget that the definition of who is or isn't a citizen and who is or isn't eligible to vote is historically impermane

Of course it was democratic. It's easy to forget that the definition of who is or isn't a citizen and who is or isn't eligible to vote is historically impermanent. It's not even comparable to women's suffrage: women were citizens who couldn't vote because of their gender, whereas slaves were in an entirely different category. The closest equivalent in the modern US would be prisoners (except their status is not intrinsic but temporary). In terms of human rights, slaves weren't really treated as human. Slaves are property, not unlike cattle and livestock. This mindset is obviously appalling from a human rights point of view, but it's misleading to call a state undemocratic just because it doesn't categorize a large segment of its population as people (the "demos" in "democratic"), even if we wouldn't consider it democratic by our (mostly superior) modern ideas of who should or shouldn't be represented in a representative democracy. The secessions happened around a time when those definitions began to change and more non-slaves became increasingly uncomfortable with the dehumanizing idea of slave ownership (in part carried by new religious ideas though it would be naive to thank religion for abolishing slavery). One of the reasons this change of mind was met less favourably in the seceding states was that they were the ones most economically dependent on slave ownership and therefore most threatened by any legislation that would make the practice illegal or less viable. Heck, considering how latent racism still is in the modern US, it should be easy to imagine how the idea that black people are no different from white people except for irrelevant details like the colour of their skin wasn't actually widely accepted at the time. It's not like free slaves were treated as equals to white men either -- although at least recognizing them as human (and citizens) certainly was an improvement.