How was most of the territory west Texas obtained by US?

Most of the territory of West Texas was obtained by the United States through the Treaty of Guadalupe Hidalgo, which was signed in 1848 to end the Mexican-American War. The treaty resulted in the United States acquiring over 500,000 square miles of territory, including the present-day states of California, Nevada, Utah, Arizona, New Mexico, and parts of Colorado and Wyoming. In addition, the United States also gained the Rio Grande Valley, which had been a disputed territory between the two countries.