. . . and six hundred thousand men were dead

The dispute that resulted in the secession of eleven Southern states from the Union and the ensuing Civil War proximately concerned the geographical expansion of slavery, but ultimately bore on the existence of the institution of slavery itself. This paper asks why in 1861 after seventy years of artful compromises over slavery civil conflict became unavoidable. The paper seeks an answer that goes beyond a description of the breakdown of compromises based on existing constitutional arrangements and that explains why attempts to negotiate a new constitutional compromise failed. Combining theoretical and historical analysis the paper concludes that in the years leading up to 1861 the outcome of the dispute over slavery had become too important to both Northern and Southern interests, relative to the expected costs of civil conflict, to be settled peacefully.