In 1848 The war against Mexico ends with the signing of the Treaty of Guadalupe-Hidalgo, which gives the United States almost half of what was then Mexico. This includes all of what is now the U.S. Southwest, plus parts of Utah, Nevada and Wyoming and most of California.The treaty guarantees citizenship rights to everyone living in these areas mostly Mexicans and Native people. It also guarantees the continued use of the Spanish language, including in education.
One hundred fifty years later, in 1998, California breaks that treaty, by passing Proposition 227, which would make it illegal for teachers to speak Spanish in public schools.
Source: The Applied Research Center