Which issue was central to the conflict between the north and the south during the decades leading up to the civil war? political party divisions states' rights foreign intervention territorial expansion

states' rights.

The issue of slavery brought up a lot about the issues of states' rights, the South supported things like nullification and slavery becoming legal in the territories. So slavery, which was so key to the South was fought for by fighting for "states' rights".

Internal combustion engines

Idk i’m not smart so yeah sorry