The secession of seven Southern states in 1860 to 1861 set in motion the train of events that led to the American Civil War. The war ultimately cost 620,000 lives, precipitated the internal collapse of slavery, prompted President Lincoln's Emancipation Proclamation, changed the Constitution, and transformed the American union of states into a nation. The destruction of slavery was arguably the greatest social revolution in American history, and it removed the most glaring contradiction to the ideals of the Founding Fathers. Union victory ensured the inviolability of the Union and supremacy of the federal government. Secession, in short, inaugurated the most transforming crisis in American history. More than any other single event, the Civil War defined modern America.

Secessionist Theory

As early as the 1820s, some southerners raised secession as a last resort to defend slavery and southern rights. The notion that any state could voluntarily leave the Union was based...