Americans began their acquisition of Mexico by simply moving there. Even after the Mexican government prohibited American immigration to Texas, Americans continued to cross the border illegally. Stephen Austin, the "Father of Texas," urged Americans to come to Mexico, "passports or no passports."
After half of Mexico was claimed by the United States in 1848, thousands of Mexicans found themselves immigrants without ever having moved. In California, they outnumbered Americans by ten to one. They were made citizens of the United States, but they would, in the decades following the Treaty of Guadalupe Hidalgo, lose most of their land to drought, squatters, taxes, and American courts.
Now, some Americans fear a reconquista of the Southwest.---Eula Biss, "Babylon" (Notes from No Mans Land: American Essays)