The year is 1830 when Mexico was free from Spain even though it gained independence between 1810 to 1821 it was in a long war with Spain for 11 years and won by getting native tribes nearby and working with them and even getting the most dangerous ones. But there were some problems when they won like they had international rebellions against Mexico being a country which put the country in financial debt and lack of funding for a country that is 4.5 million square kilometers. Then all hell broke loose in 1846 when America wanted to take big pockets of land from Mexico, which was one of the biggest countries in the entire world. Mexico said no then on April 25th 1846 The United States declared war on Mexico.
In June 1846 U.S. troops pushed Mexican soldiers to southern California. Then a month later in June U.S. troops pushed Mexican troops back into Mexico then the U.S. had full control of California.
Some Neighboring native American tribes went to war with the U.S and some with Mexico but mainly were on the side of the United States. There was a big pocket of land named Tejas/Texas it soon became a republic in 1837 The U.S and Mexico wanted the land. Tejas was a place where native American tribes stayed and where they were squeezed in and a lot of Mexican farmers worked in Tejas to stay as far away from the Mexican government as possible because of how corrupt it was and failed.
Throughout the war for Tejas independence from Mexico the Tejanos and whites worked well together as allies. The whites and Tejanos were fighting together in the Alamo. Then the Mexican-American war ended on February 2nd 1848.
When the war was over white plantation owners from Virginia, Mississippi and Georgia came to Tejas and stole over 300 Tejanos farms and then turned them into ranches and plantations using slaves. Southern plantation owners imported racism and segregation between whites and Tejanos. Once the slave economy came to Tejas they ruined the relationship with white and Tejano and made the whites look bad to the Tejanos and the slave economy brought racism.