The history of California can be divided into the Native American period, the European exploration period (1542–1769), the Spanish colonial period (1769–1821), the Mexican period (1821–1848), and United States statehood. California was one of the most culturally and linguistically diverse areas in pre-Columbian North America. After contact with Spanish explorers, many of the Native Americans died from foreign diseases. Finally, in the 19th century there was a genocide by United States government and private citizens, which is known as the California genocide.

The California genocide was a series of systematized killings of thousands of Indigenous peoples of California by United States government agents and private citizens in the 19th century. It began following the American Conquest of California from Mexico, and the influx of settlers due to the California Gold Rush, which accelerated the decline of the Indigenous population of California. Between 1846 and 1873, it is estimated that non-Natives killed between 9,492 and 16,094 California Natives. In addition, between several hundred and several thousand California Natives were starved or worked to death. Acts of enslavement, kidnapping, rape, child separation and forced displacement were widespread. These acts were encouraged, tolerated, and carried out by state authorities and private militias.