How did the us attain their southern border?

The United States attained its southern border primarily through a series of territorial acquisitions and conflicts. The 1846-1848 Mexican-American War resulted in the U.S. gaining significant territories, including present-day California, Arizona, New Mexico, and parts of Colorado, Nevada, and Utah, solidifying the southern boundary. Additionally, the Gadsden Purchase in 1853 further defined the southern border by acquiring land from Mexico to facilitate a southern transcontinental railroad. These events collectively shaped the current U.S.-Mexico border.