The Republic of Mexico’s Constitution, adopted in the 1820s, forty years before the American Civil War, prohibited slavery. By 1846, all mission neophytes had been freed from the mission system and the mission lands had been secularized. Mexican-appointed governors chose administrators for each California mission to give the land and livestock to some mission neophytes and many rancheros.
American settlers moved into the California territory with Native American and Black slaves after 1840. They never became Mexican citizens or bowed to Mexican laws. In 1846, several American men staged a revolt in Sonoma to make California a republic with their laws. They were named the Bear Flaggers for the flag they created for their republic. Many of these rebels were quite drunk, and some people thought the bear painted on the flag looked more like a pig, but the Americans pulled down the Mexican flag and saluted the new California Republic flag. Now they could keep their enslaved workers and their land without bowing to Mexico.
The United States Pacific Naval Squadron annexed Alta California a few weeks later, and the California Republic flag was lowered and replaced with the Stars and Stripes. When California became a state in 1850, it joined the Union as a free state. Until the Civil War, some enslavers kept it secret from their workers that they were now legally free.
Because several state flags have a pro-slavery history, many flag enthusiasts see it as a disturbing problem and want to change them.