The area that is now California was originally claimed by Spain. It was part of the Spanish territory known as Alta California, established as a province of New Spain in 1804. After Mexico gained independence from Spain in 1821, California became a territory of Mexico until it was ceded to the United States in 1848 following the Mexican-American War. The formal annexation of California by the U.S. occurred after the Treaty of Guadalupe Hidalgo in 1848.
