Timeline of American Territorial Expansion

From 13 Colonies to Continental Nation

American expansion unfolded in distinct phases across the 19th and early 20th centuries.

Phase 1: Early Republic (1783-1840s)

• 1783: Treaty of Paris — independence to Mississippi River
• 1803: Louisiana Purchase — 828,000 sq mi from France ($15M)
• 1819: Adams-Onís Treaty — Florida from Spain
• 1845: Texas Annexation — Republic of Texas joins Union

Phase 2: Continental Completion (1840s-1860s)

• 1846: Oregon Treaty — 49th parallel with Britain
• 1846-48: Mexican-American War — Mexican Cession (CA, NV, UT, AZ, NM, CO)
• 1853: Gadsden Purchase — Southern AZ/NM rail route ($10M)
• 1867: Alaska Purchase — "Seward's Folly" from Russia ($7.2M)

Phase 3: Overseas Empire (1890s+)

• 1898: Spanish-American War — Puerto Rico, Guam, Philippines
• 1898: Hawaii Annexation — Republic of Hawaii → Territory
• 1917: Virgin Islands Purchase — from Denmark ($25M)

Mechanisms

Purchase, treaty, annexation, conquest, settlement. Driven by Manifest Destiny ideology, economic opportunity, security concerns, and great power competition.