From June 1846 through January 1847, the Army of the West, commanded by Brigadier General Stephen Watts Kearny, marched from Fort Leavenworth, Kansas to San Diego, California, annexed New Mexico and Arizona without firing a shot, and gained California for the United States after three engagements. During the campaign, Kearny's command varied in size from 1,700 Missouri volunteers and U.S. Army Dragoons to fewer than two hundred soldiers, sailors, and marines, and California volunteers. Histories of the campaign have focused on the Battle of San Pasqual and General Kearny's orders before and during the battle in an attempt to explain why things went poorly for United States forces. Kearny's campaign provides tremendous insight into the operational level of war, tactical actions linked toward the accomplishment of strategic goals, because he achieved robust territorial gains that facilitated the United States' expansion to the Pacific Ocean with small and diverse forces.