- Land disputes: The border between the United States and Mexico was disputed after Mexico gained independence from Spain in 1821. Texans wanted to expand their territory into what was then Mexican territory.
- Political and social differences: Texans were mostly American settlers who wanted to live under their own laws. Texas had been part of Mexico since 1821, but many Texans felt that the Mexican government was oppressive and did not respect their rights.
- Economic conflict: American settlers often took over land that was already owned by Mexican landowners, which created conflict between them.
- Texas War for Independence: The Texas War for Independence began in 1835 when Texans revolted against Mexican rule. The war lasted until 1836, and Texas emerged as an independent republic.
- U.S. Annexation of Texas: In 1845, the United States annexed Texas, which led to the Mexican-American War. The war lasted until 1848, and the United States won, gaining control of all of the Mexican Cession including the present-day states of Arizona, California, Colorado, Nevada, New Mexico, Texas, and Utah.