Why according to one historian were Mexican Americans in the mid-1800s foreigners in their native land?

According to historian David G. Gutiérrez, Mexican Americans in the mid-1800s were considered foreigners in their native land due to the aftermath of the U.S.-Mexico War and the Treaty of Guadalupe Hidalgo, which resulted in the U.S. acquiring vast territories previously belonging to Mexico. This shift in sovereignty led to a legal and social marginalization of Mexican Americans, as they faced discrimination, land dispossession, and the imposition of Anglo-American cultural norms. Despite their long-standing presence in these regions, they were often viewed as outsiders, leading to their alienation in a land they had historically inhabited.