Lol negotiating. Lincoln couldn't do anything that would have ended the war. Cause the only way the south would have ended the war was some kind of constitutional amendment allowing slavery. That wasn't happening.
There were 3 results caused by the actions of the south
1. Let them secede. In the end maybe not the worst option. The slave labor method would have almost for sure ruined their economy. And then we could have happily accepted thme back into the union when Mexico or Britain invaded them.
2. Give in to their demands. Not happening. They had no leg to stand on. We had the upper hand.
3. Go to war.
As far as your "call for volunteers" thing, yes that was the last straw for a few states. But it wasn't done without cause. As the confederates refused Lincoln's aid to the FOrt then began attacking it. It's not like the south just said, we're seceding and Lincoln started mustering troops. In fact the opposite happened. the First 7 states to secede then went on to start raising a 100,000 troop army. After the confederates started raising an army, started blockading union forts in the south, and then attacking one of them, what do you think is a rational response from Lincoln? Oh sorry you're cool keep raising an army and attacking us, we'll jsut sit back and try to convince you to stop.
I still love when you said the war wasn't about slavery, that's my favorite.