"Manifest Destiny" — coined by journalist John L. O'Sullivan (1845) — the belief that America was divinely destined to expand from the Atlantic to the Pacific. It justified territorial acquisition, Native American displacement, and war with Mexico.
The Central Tension: Every new territory forced the question: FREE or SLAVE? Expansion didn't just grow America — it TORE IT APART, directly causing the Civil War.
Territorial Growth
1803
Louisiana Purchase
1845
Texas Annexation
1848
Mexican Cession
1867
Alaska Purchase
Tags
Manifest DestinyOregon TrailTrail of TearsGold RushHomestead ActRailroad
Expansion Themes
AP Exam Focus (KC 4.3 / 5.1): Key themes: (1) Manifest Destiny as ideology justifying expansion, (2) Louisiana Purchase DOUBLING U.S. size, (3) Indian Removal Act as federal ethnic cleansing, (4) Mexican-American War as war of conquest, (5) Oregon Trail as the "Great Migration," (6) Gold Rush transforming California, (7) Homestead Act + Railroad = settling the Great Plains, (8) EVERY acquisition triggering slavery debate → Civil War.