How the U.S. Expanded Its Borders in the 1800s: 6 Major Acquisitions

1. Louisiana Purchase (1803)

$15M from France. 828,000 mi². Mississippi River to Rockies, Gulf to Canada. Doubled US size.

2. Florida Cession / Adams-Onís Treaty (1819)

Spain cedes East & West Florida. US assumes $5M claims. Defines US-Spain (later Mexico) boundary to Pacific.

3. Texas Annexation (1845)

Republic of Texas joins as 28th state. Precipitates Mexican War.

4. Oregon Treaty (1846)

US/UK split at 49th parallel. US gains WA, OR, ID, parts of MT/WY. "54-40 or Fight" resolved.

5. Mexican Cession (1848)

Treaty of Guadalupe Hidalgo ends Mexican War. US pays $15M + assumes claims. Gains CA, NV, UT, AZ, NM, CO, WY.

6. Gadsden Purchase (1853)

$10M to Mexico for southern AZ/NM strip (30k mi²) — southern transcontinental railroad route.

7. Alaska Purchase (1867)

$7.2M from Russia ("Seward's Folly"). 586k mi². Strategic, resource-rich.

Summary

From 890k mi² (1790) to 3.1M mi² (1867) — +250%. Driven by Manifest Destiny, slavery politics, commerce, security, diplomacy.