2. The Road to Disunion, Volume II: Secessionists Triumphant 1854-1861Among the classics (including those of Kenneth Stampp), Potter's book is a pretty much undisputed masterpiece.
by William W. Freehling (2007).
3. Lincoln and the Decision for War: The Northern Response to SecessionFreehling's dense and often brilliant tome picks up where his The Road to Disunion, Vol. 1: Secessionists at Bay, 1776-1854 (1990) left off. Contingency was a popular theme at the time (also heavily influencing Nelson's Lankford's excellent Cry Havoc!: The Crooked Road to the Civil War, 1861), and Freehling's book perhaps most interestingly shows how random events and the timing of individual actions influenced the nation's path toward secession and war.
by Russell McClintock (2008).
4. The Fate of Their Country: Politicians, Slavery Extension, and the Coming of the Civil War by Michael F. Holt (2004).McClintock's book gauges the northern public's reaction to secession by examining the views of a large number of thought leaders across a trio of states representing three major regions [Mid-Atlantic, New England, and Old Northwest]. Even better is the study's demonstration of how partisan party politics and patronage shaped President Lincoln's political options and his strategy for dealing with secession. Nearly a decade on, McClintock may also have to assume a spot on my Civil War one-hit-wonder list, too.
5. Clash of Extremes: The Economic Origins of the Civil War by Marc Egnal (2009).Holt's slim volume is a wonderfully incisive politico-centric summary of the territorial debates in Congress. His interpretation emphasizes shortsighted partisan political maneuvering and the breakdown of the two-party system as key driving forces behind the breakup of the nation.
I was going to reserve this last spot for a study of the Sumter crisis but really wanted to fit Egnal's book in here somewhere. It contains some really original and well thought out views on underlying regional and national economic forces that moved the sections apart, while also not losing sight of slavery's fundamental place among the forces involved.