How did California become part of the United States?

California became part of the United States through the Mexican-American War, which concluded with the Treaty of Guadalupe Hidalgo in 1848. This treaty ceded a vast territory, including all of present-day California, from Mexico to the United States. The Gold Rush, beginning in 1848, significantly accelerated settlement and led to California's admission as a U.S. state on September 9, 1850, as part of the Compromise of 1850.21345