Manifest Destiny drove America westward with relentless force. The Louisiana Purchase doubled the nation's territory overnight. Lewis and Clark mapped the unknown. The Oregon Trail carried hundreds of thousands of settlers across plains, mountains, and deserts. Gold rushes sparked mass migrations. And through it all, the nation confronted a deepening moral contradiction — a republic founded on liberty was systematically displacing the peoples who had lived on this land for millennia. By 1860, America stretched from sea to sea, but the tensions over slavery that westward expansion had exposed were about to tear the country apart.