Why did I not know that this had been published?
William W. Freehling (2007), The Road to Disunion, Volume II: Secessionists Triumphant 1854-1861 (Oxford: Oxford University Press: 0195058151).
Admittedly, it is seventeen years since he published volume I of The Road to Disunion: Secessionists at Bay. Nevertheless, I thought it would have made a bigger splash. If it is 1/2 as good as its predecessor, it is the must-read history book of the year.