Was the Civil War necessary?

I think Jefferson Davis miscalculated when he fired the first shot.

Upon secession, manifest destiny became complete, a free labor industrial North from California to New York City, bridged by Chicago.  European immigration took off, new immigrants did not need to compete in a rigged labor market.

This was visible to Davis after the secession and before the first shot. Slavery was not that institutionalized in Texas. The slave south was boxed in, the borders economically and militarily defenseless. Jefferson Davis should have paused.  Robert Lee should have known their position was precarious, and advised early for negotiations.  Their better move at the time was to negotiate for re-unionisation, with a buyout clause for slavery. That was their best move from what they saw, they blundered.

Lincoln would have grabbed the carrot, the reunionization was not that far from his original position, he would have negotiated under blackmail and gave the secessionists better terms. Lee and Davis blew the call, even as advocates for racism, they still blew the call from their point of view at the time.