This is not true. As David Orland wrote:
As a matter of fact, the American Southwest was not, as MEChA claims, “stolen” from Mexico. Following the Mexican-American War, the government of Mexico legally ceded this territory to the United States (by the Treaty of Guadalupe de Hidalgo, 1848). Nor has there ever been any place called “Aztlan” on American soil, much less a “Nation of Aztlan.” Invented 30 years ago by radical Latino activists, the Nation of Atzlan has more in common with Atlantis than with Israel. [...] MEChA plans for the American Southwest is to be a peaceful one — at least for the time being. By supporting continued high levels of Mexican immigration to the United States, MEChA hopes to achieve by sheer weight of numbers what the U.S. government long ago achieved by force of arms: the re-partition of the American Southwest. To this end, MEChA endorses a cocktail of pro-immigration policies. These include open borders, government benefits (including the right to vote and obtain drivers licenses) for non-citizens, amnesty for illegal aliens, dual citizenship, state recognition of Spanish as an official language, and racial set-asides in education and corporate hiring.
The membership of MECHA includes many prominent Democrat polticians, and the Democat Party panders for the "Aztlan"/Mexican-American vote by supporting policies which aid the accomplishemnt of the "reconquesta" goals.
If America continues its lax policies - allowing "Immigration without assimilation" then America is committing cultural suicide. We MUSTN'T let Mexicans do to us what Muslims are doing to Holland and France and Europe: conquer it by insidious invasion of their underclass and by the ensuing demographics.