Because the South attacked the Federal troops on the Federal base at Ft. Sumter.
No, because Lincoln and the Northern business interests he repped for (remember, Lincoln was a railroad lawyer, not an abolition lawyer or a civil-rights lawyer) were determined to drag the Southern States back into the Union by force.
The Northern economic-development model required a payor (street synonym: chump). The South was the payor. They couldn't leave. If they did, the Northerners would have to pay for their own development, which was a nonstarter for them.
ROTFLMAO.