Westward Expansion: Louisiana Purchase to Manifest Destiny
Between 1803 and 1853, the US grew from 13 states clustered on the Atlantic to a continental nation. Master the four major land acquisitions and the ideology behind them.
From sea to shining sea
In 50 years, the United States tripled in size. Five major events made that happen, and the CBE asks about every one.
- Louisiana Purchase (1803) — bought from France (Napoleon needed cash for European wars). Doubled the size of the US for $15 million. Stretched from Mississippi River to Rocky Mountains.
- Florida Cession (1819) — acquired from Spain via the Adams-Onís Treaty.
- Texas Annexation (1845) — Texas was independent after winning revolution from Mexico (1836); annexed to the US in 1845.
- Oregon Country (1846) — split with Britain at the 49th parallel.
- Mexican Cession (1848) — won in the Mexican-American War. Includes modern California, Nevada, Utah, Arizona, and parts of New Mexico/Colorado/Wyoming.
- Gadsden Purchase (1853) — small strip along southern Arizona/New Mexico, bought from Mexico for railroad route.
Manifest Destiny — the ideology
Manifest Destiny was the 19th-century belief that the US was destined by Providence to expand from Atlantic to Pacific. Coined by journalist John O'Sullivan in 1845, it provided moral cover for territorial expansion — including the Mexican-American War. The ideology had a dark side: it ignored the rights of Native Americans and Mexicans already living on the land.
Mason-Dixon and the slavery question
Every new territory raised the same explosive question: slave or free? The Mason-Dixon Line originally surveyed in the 1760s as a colonial boundary; it became the symbolic dividing line between northern free states and southern slave states. Compromise after compromise (Missouri Compromise 1820, Compromise of 1850, Kansas-Nebraska Act 1854) kicked the can down the road until the Civil War made it permanent.