A disputed strip of Texas borderland erupts into ambush, and within two years American armies are fighting on three fronts — Zachary Taylor’s campaign into northern Mexico, the overnight conquest of California, and Winfield Scott’s march from Veracruz to Mexico City — while in Washington a tax resister, a rider on a funding bill, and a freshman congressman turn the war into the opening argument of the fight over slavery that will not be settled until the Civil War. (Texas annexation and the treaty’s territorial terms are covered in full in this archive’s Trail & Territory volume.)