What are the Causes of the US Civil War?

Answer 1

Growing friction between the rural slave-owning South and the industrial North which would not have been able to use slaves, even if they had them.

As it was getting harder to create new slave-states, the South were in danger of getting out-voted in Congress, which would then pass laws unfavourable to them.

The huge profits of the cotton trade made the South feel strong enough to break away and form their own nation.

The North felt strongly about the sanctity of the Union - which largely meant that they didn't want to lose the cotton revenues. (They were not principally fighting for Abolitionism at this stage.)