The 1848 Treaty of Guadalupe Hidalgo that ended the Mexican American War guaranteed U.S. citizenship and legal protection for those hundreds of thousands of Mexicans already inhabiting the numerous territories that were changing hands. But in practice, those protections were time and again denied to Mexican landowners, in favor of Anglo squatters and thieves who took the land they desired and bent the laws to support their crimes. If you go back a little further, those lands were populated by dinosaurs, but we don't live in those times either. We live in today's world and should worry about the current situation.