They would be able to sell what they made overseas in any case. A tariff might cut into foreign goods that they could buy, but if that was really important to them, they could have stayed and fought the tariff. Rates would have gone up, but nowhere near as much as they eventually did.
Slavery was a side issue at best and Lincoln did not care one way or the other although it was a tool to stick to to the Confederates.
Bleeding Kansas? John Brown? Dred Scott for that matter? Was all that about trade and tariffs? Slavery -- the expansion of slavery -- was the big issue of the 1850s.
I guess it all depends on what you believe and who writes the history, since the South lost, sometimes they were seen as the villains. It really comes down to two things, who won and whose ox is being gored.
The victors write the history. But the vanquish write the legends and myths. Except in this case, an awful lot of "Northern victor's history" was written from a very pro-Southern point of view. Whatever historians are saying now, for over fifty years in the early 20th century they were a lot friendlier to the secessionists than Northerners at the time were or Americans today are.
I still think on the trade and States rights issues, the Confederates were right. Chattel slavery was dying, I think the Confederates would have given it up around the time Brazil did, the 1880s, certainly by 1900 or if your an extreme pessimist, 1920s.
Maybe, maybe not. That is a long time if you are a slave. And what replaced slavery would have been pretty similar. But that big historical clock that has Brazil abolishing slavery in the 1880s may have been a result of our Civil War. If the slave owners had won, it might well have set back abolition in other countries.
As to the two countries living side by side, who knows, maybe over time, it would be like the US and Canada and had WWI and WWII happened without too many butterflies, we could have been allies, Im sure we would have been during the Cold War.
Not so sure. There was going to be a major race conflict in the South at some point and who's to say how that would have turned out.
A lot of southerners have come to consider as vindication what northerners only intended as mercy and politeness. This can always be seen when the subject of Jefferson Davis being released without trial comes up.