John C. Fremont led an unauthorized expedition into Mexican territory in Alta California and helped settlers there declare independence as the Bear Flag Republic. Stephen Kearney marched troops from Kansas to New Mexico and California to take control of the territories. Several key figures played roles in the war, including James K. Polk who pushed for war over the Texas border dispute, Zachary Taylor and Winfield Scott who led military victories, and Antonio Lopez de Santa Anna who initially went into exile but returned to lead Mexican forces until being forced to sign the Treaty of Guadalupe Hidalgo, ceding California and New Mexico to the US.