The war was fought over the third issue.

The North went to war to stop the South seceding, true enough.

But the reason the South tried to secede was to preserve slavery, which it (wrongly) thought was under threat.

Basically it was, in a sense, a misunderstanding.

I think it likely that if the South had been allowed to secede, slavery would have been ended within a generation, as happened in Brazil, and the outcome could well have been a country with a prevailing attitude towards race more akin to Brazil than to the post-civil-war South.

Who knows? It's all airy speculation, with no answers. Nothing worth getting excited about at this distance of time.