California Admitted as 31st US State

California was admitted to the Union on September 9, 1850, as a free (non-slave) state — a direct consequence of the Wilmot Proviso debate sparked by the Mexican-American War. Its admission as a free state was part of the Compromise of 1850. The Gold Rush had brought 300,000 people to California by 1855, making it one of the most consequential of America's territorial acquisitions. California's statehood reignited the sectional crisis over slavery expansion that led to the Civil War.