The thing about alternative history is, you can't just imagine one big thing changed, and then assume that all the other places stay in place.

For example, if you assume victory for the British and those Americans who were opposed to secession, that victory would have included the estimated 20,000 black slaves who fought on the British side to win their freedom. That could have significantly strengthened the abolitionist cause back in England - and arguably it might have weakened it in the Northern colonies, if there continued to be strong secessionist feelings..

If strengthened abolitionism is envisaged in Britain, while a French Revolution is still seen as to occuring, a second more successful attempt at secession, while England was overstretched elsewhere, can be imagined. But with the difference that the defence of the institution of slavery would have been the key issue.

Thus, rather than slavery being seen as an embarrassing anomaly, confined to part of a new United States, and in conflict with aspirations of liberty for all, it could have been seen as a fundamental founding element of the new country. Perhaps the constitution would have had an Amendment guaranteeing "The right to own black slaves". And perhaps a Declaration of Independance declaring that the truth which was self-evident was that "All white men are created equal."