Mexican American history, or the history of American residents of Mexican descent, largely begins after the annexation of Northern Mexico in 1848, when the nearly 80,000 Mexican citizens of California, Nevada, Utah, Arizona, Colorado, and New Mexico became U.S. citizens. Large-scale migration increased the U.S.’ Mexican population during the 1910s, as refugees fled the economic devastation and violence of Mexico’s high-casualty revolution and civil war. Until the mid-20th century, most Mexican Americans lived within a few hundred miles of the border, although some resettled along rail lines from the Southwest into the Midwest.