The South is called the Confederacy, and the North is called the Union. The Confederacy was reliant on slaves and farming, whereas the North was reliant on manufacturing. The North wanted slavery, and the South wanted to keep it.
The South rode on farming with slaves, while the North had the industry, so by taking the slaves, the North's economy would crumble. Another reason is that the South left because they wanted to keep and expand slavery, but the North had the power to defer it, and they did.
The Southwest was highly reliant on agriculture