r<br >YO<br >AMI~:RI CA<br >Why Do They Leave?<br >The First Mexican Americans<br >he United States has been built by immigrants who have flocked<br >to North America since Colonial days. Yet for many years before<br >the first Pilgrims landed at Plymouth Rock， Mexicans already<br >lived in the Rio Grande Valley of what is now Texas. So the first<br >Mexican "immigrants" to the United States were not really immi-<br >grants at all. As aborigines and descendants of the conquistadores， they<br >were residents of the part of Mexico that became United States territory after<br >the Mexican-American War. Indeed， what is now California， New Mexico，<br >Arizona， Texas， and Colorado was once all part of a very large Mexico.<br > In 1821 Mexico declared its independence from the Spanish<br >colonial rule that had existed for 300 years. TWenty-four years<br >later the United States annexed the fledgling Republic of Texas，<br >ending nine years of Texan independence. Then， with the Treaty of<br >Guadalupe Hidalgo， signed in 1848 to end the Mexican-American<br >War， and the Gadsden Purchase of 1853， the United States<br >acquired territory constituting nearly half of Mexico. The Mexican<br >residents of this land became the first Mexican Americans.<br > Mexican Americans go by many names in America.<br >Mexicans who leave Mexico are emigrants， but when they get to<br >their new country， they become immigrants (leaving a country is<br >emigrating; coming to a<br >lish themselves as resi(<br >Mexican Americans， and<br >ond-generation Mexica[<br >Americans are pa~t of t]<br >includes Puerto Ricans， (<br >all other Spanish-speakin<br > Much of the land t<br >Mexican-American Wa<br >landowners， or ranchero<br >that had been theirs for~<br >New American settlers.<br >