So, you believe that the only tool of negotiation is the rifle.
When you and your neighbors have a difference of opinion, do you just start popping caps at each other?
Lincoln needed a war. The South didn't. The South and Lincoln recognized that the South didn't have the industrial infrastructure to support such an endeavor. The South wanted to be able to govern themselves without northern interference..............and we still do.
No, but apparently the CSA was under this impression, which is why they chose to start the shooting by attacking a federal installation that had already stated it would be forced to surrender in a few days anyway.
Davis knew exactly what he was doing at Sumter. The CSA, at the time, consisted of 7 states, all in the Deep South and almost exclusively agricultural. There was no way this was a viable nation.
The CSA needed at least some, hopefully all, of the other 8 slave states to be able to withstand a confrontation with the Union. There were strong pro-Union movements in each of them, and in the days before polling nobody really knew what public opinion was.
Davis ordered the shooting to start as a way of forcing these states to pick a side. If all went with the CSA, secession would have succeeded, as even Lincoln later agreed.
If all stayed with the Union, the war would have been over quickly and relatively bloodlessly. In fact, it's likely some of the seceded states would have chickened out and "unseceded," as other southern states abandoned SC during its earlier confrontation with Jackson.
As it happened, four slave states (MO, KY, MD, DE) eventually stayed in the USA; three joined the CSA (AR, NC, TN) and one (VA) split in two.
This did not give the CSA enough resources to be able to win, but it gave it enough to fight bloodily for 4 years, with over 600k Americans being killed.
On news being received of the fighting at Sumter, VA immediately seceded, despite the convention having rejected secession a couple days before. Please note that VA received news of an attack by the CSA on the USA, not the other way around. So Davis' ploy succeeded.