The Treaty of Guadalupe Hidalgo ended the Mexican War in 1848.

The Treaty of Guadalupe Hidalgo, between the United States and Mexico, marked the end of a border dispute that began in May of 1846 with the secession of Texas from Mexico and its annexation by the United States. By the terms of the treaty, Texas, which had been part of the United States until it was ceded to Spain in negotiations for Florida in 1819, once again became part of U.S. territory, along with present-day Arizona, California, New Mexico and parts of Colorado, Nevada and Utah.

Smithsonian's History Explorer
In a section of the online exhibition The Price of Freedom:  Americans at War, students learn about  The Mexican War (4-12)  by first examining its causes, Texas's struggle for independence, and the controversial concept of Manifest Destiny. They then examine the war's major events and battles and the results of the Treaty of Guadalupe Hidalgo. 

Xpeditions
Students investigate the characteristics of the United States-Mexico border in the Xpeditions lessonWhat's it Like to Live Along a National Boundary? (3-5).