US Acquisition of New Mexico & Arizona (1846): Mexican War & Kearny's Campaign

The U.S. acquired New Mexico and Arizona during the Mexican–American War (1846–1848):

Causes

• Texas annexation dispute (1845)
• Boundary disagreements (Nueces vs. Rio Grande)
• Manifest Destiny expansionism
• Slavery expansion tensions

Military Campaign (1846)

• April 1846: War declared
• August 1846: Gen. Stephen W. Kearny occupies Santa Fe (NM capital) bloodlessly
• December 1846: Kearny enters Arizona; January 1847 occupies Tucson
• Provisional governments established in both territories

Treaty of Guadalupe Hidalgo (Feb 2, 1848)

• Mexico ceded 525,000 sq mi (55% of territory)
• US paid $15 million
• Included NM, AZ, CA, NV, UT, parts of CO, WY, KS

Aftermath

Rapid American settlement, territorial governments, demographic shift. By 1860: 100,000+ population. Statehood: NM (1912), AZ (1912).