1846-1848: The Mexican American War

Following the end of the Mexican-American War (1846-1848), in which Mexico was defeated, the Treaty of Guadalupe Hidalgo granted America the land of California, Texas, parts of Colorado, Arizona, New Mexico, Utah and Nevada.¹ Tens of thousands of Mexicans thus became residents of the U.S.² After the Chinese Exclusion Act of 1882, around 1890, Mexicans migrated to the U.S., being recruited by the U.S. railway companies due to labor shortages.³  In many cases, they freely moved across the border for temporary jobs and then returned home. 

Sources:

1. “Becoming Part of The United States,” Library of Congress, accessed June 8, 2021 https://www.loc.gov/classroom-materials/immigration/mexican/becoming-part-of-the-united-states/ 
2. Ibid.
3. “U.S.-Mexico Relations 1810-2010,” Council on Foreign Relations, accessed June 9, 2021, https://www.cfr.org/timeline/us-mexico-relations