The U.S.–Mexico Border Dispute Over Texas

The dispute centered on the southern boundary of Texas after its independence (1836) and U.S. annexation (1845).

Competing Claims

• Mexico: Border at the Nueces River (north of the Rio Grande).
• U.S.: Border at the Rio Grande (further south), based on Texas's claim as a republic.

Escalation

President Polk sent troops into the disputed territory (1846); Mexican forces attacked, triggering the Mexican–American War (1846–1848).

Resolution

The Treaty of Guadalupe Hidalgo (1848) set the border at the Rio Grande. Mexico ceded the Mexican Cession (California, Nevada, Utah, most of Arizona, parts of Colorado, New Mexico, Wyoming) for $15 million.