Smith1776 wrote: ↑Sat Jun 05, 2021 8:54 pm
Yeah, it was definitely about slavery. Although it wasn't about full on
emancipation till its later stages.
The simplistic answer is rarely the right one. Even asking the question isn't so easy. For example, by "the war" are we talking about secession, or the raising and deployment of armies?
Secession wasn't a monolithic event. Taking a very simplified look, there were multiple batches: first there was the batch of states which seceded after the election of Lincoln. Here's where you can argue that they left because of slavery. The other batch didn't secede until after Lincoln raised an army to attack their neighbors. Can you say that those states were seceding and/or fighting primarily because of slavery? That's a harder argument to make.
Also, issues take place on multiple levels. There were definitely other issues besides slavery: the tariffs used to fund the federal government were mostly paid by the South, just for one example. But even if slavery were the only issue, there's a meta-issue, which is what's the role of the federal government in determining the civic order in the states. The proximate issue may be slavery, but the meta-issue is whether or not the states are vassal sub-units of the federal government. In this way, the issue can be both slavery and not-slavery at the very same time.
As far as "preserving the union": a voluntary union can never be preserved by force. It can be changed into a completely different kind of union, which is what happened.
Lincoln was perfectly willing to let slavery continue: he was willing to support the Corwin Amendment, a proposed 13th Amendment which would explicitly permanently allow slavery, in exchange for the South not leaving. Why did he care so much about preserving the union? See above: the tariffs that funded the federal government were paid by the South.