Answer:
During the Mexican–American War, Frémont was a major in the U.S. Army. He took control of California from the California Republic in 1846.
Step-by-step explanation:
John C. Frémont, in full John Charles Frémont, (born January 21, 1813, Savannah, Georgia, U.S.—died July 13, 1890, New York, New York), American military officer and an early explorer and mapmaker of the American West, who was one of the principal figures in opening up that region to settlement and was instrumental in the U.S. conquest and development of California. He was also a politician who ran unsuccessfully for the U.S. presidency in 1856 as the first candidate of the newly formed Republican Party.