Mexican-American War Raises Specter of Slavery's Expansion

The Mexican-American War (1846–48) conquers 525,000 square miles of territory. Black leaders and abolitionists including Frederick Douglass condemn it as a slaveholders' war of expansion. The Treaty of Guadalupe Hidalgo transfers California, New Mexico, Arizona, Nevada, Utah, and Colorado to the US, immediately triggering the agonizing question: will slavery extend into all of it?