Exploring a critical lesson about our nation that is as timely today as ever, Decade of Disunion shows how the country came apart during the enveloping slavery crisis of the 1850s.

The Mexican War brought vast new territories to the United States, which precipitated a growing crisis over slavery. The new territories seemed unsuitable for the type of agriculture that depended on slave labor, but they lay south of the line where slavery was permitted by the 1820 Missouri Compromise. The subject of expanding slavery to the new territories became a flash point between North and South.

First came the 1850 compromise legislation, which strengthened the fugitive slave law and outraged the North. Then in 1854, Congress repealed the Missouri Compromise altogether, unleashing a violent conflict in “Bleeding Kansas” over whether that territory would become free or slave. The 1857 Dred Scott decision—abrogating any rights of African Americans, enslaved or free—further outraged the North. And John Brown’s ill-planned 1859 attack at the federal arsenal at Harpers Ferry stirred anger and fear throughout the South.

Through a decade, South Carolina, whose economy depended heavily on slave labor, struggled over whether to secede in a stand-alone act of defiance or to do so only in conjunction with other states. Meanwhile, Massachusetts became the country’s antislavery epicenter but debated whether the Constitution was worth saving in the effort to abolish bondage. Both states widened the divide between North and South until disunion became inevitable. Then, in December 1860, in the wake of the Lincoln election, South Carolina finally seceded, leading the South out of the Union.

Beginning with the deaths of the great second-generation figures of American history—Calhoun, Webster, and Clay—Decade of Disunion tells the story of this great American struggle through the aims, fears, and maneuvers of the subsequent prominent figures at the center of the drama, with particular attention to the key players from Massachusetts and South Carolina.

This history is a sobering reminder that democracy is not self-sustaining—it must be constantly and carefully tended.