Many American slaves used the Underground Railroad to escape to freedom in the North, but thousands of people in the south-central United States instead crossed the southern border into Mexico, where slavery was abolished in 1837. Southerners hoped that annexing Texas and invading Mexico in the 1840s would stop runaways and secure slavery's future. As Alice Baumgartner explains in this Lincoln Prize finalist, the seizure of Alta California and Nuevo México upset the delicate political balance between free and slave states, hastening the outbreak of the Civil War.

"Baumgartner debuts with an eye-opening and immersive account of how Mexico's antislavery laws helped push America to civil war…. This vivid history of 'slavery's other border' delivers a valuable new perspective on the Civil War."—Publishers Weekly