United States Occupies California and the Southwest

During the Mexican War, the federal Army of the West was charged with occupying New Mexico and California. Led by Stephen Watts Kearny, the army divided strategically into units that separately conquered Santa Fe, Taos, and southern California territories, winning the entire region for the United States.

Summary of Event

When the United States declared war on Mexico in May, 1846, the military strategy of President James K. Polk and his advisers was to occupy the capitals of the northern Mexican provinces and to march on Mexico City Mexico City;U.S. occupation of . Polk hoped the two campaigns would result in a quick end to the war. He assigned the task of occupying New Mexico and California to the Army of the West, commanded by Brigadier General Stephen Watts Kearny. In the spring of 1846, Kearny assembled his forces at Fort Leavenworth. Under his command were three hundred regular dragoons and five hundred Mormon youths, led by Lieutenant Colonel Philip St. George Cooke Cooke, Philip St. George , who had been recruited from their encampment at Council Bluffs, Iowa, where Brigham Young was making plans to move westward to Deseret. Kearny also was accompanied by a regiment of infantry and a train of wagons. Missouri frontiersmen and recruits brought the total personnel under his command to twenty-seven hundred. California;U.S. occupation of
Mexican War (1846-1848);postwar settlement
Kearny, Stephen Watts
Frémont, John C.
[p]Frémont, John C.;and California[California]
[kw]United States Occupies California and the Southwest (June 30, 1846-Jan. 13, 1847)
[kw]Occupies California and the Southwest, United States (June 30, 1846-Jan. 13, 1847)
[kw]California and the Southwest, United States Occupies (June 30, 1846-Jan. 13, 1847)
[kw]Southwest, United States Occupies California and the (June 30, 1846-Jan. 13, 1847)
California;U.S. occupation of
Mexican War (1846-1848);postwar settlement
Kearny, Stephen Watts
Frémont, John C.
[p]Frémont, John C.;and California[California]
[g]Mexico;June 30, 1846-Jan. 13, 1847: United States Occupies California and the Southwest[2430]
[g]United States;June 30, 1846-Jan. 13, 1847: United States Occupies California and the Southwest[2430]
[c]Expansion and land acquisition;June 30, 1846-Jan. 13, 1847: United States Occupies California and the Southwest[2430]
[c]Wars, uprisings, and civil unrest;June 30, 1846-Jan. 13, 1847: United States Occupies California and the Southwest[2430]
Cooke, Philip St. George
Polk, James K.
[p]Polk, James K.;and Mexican War[Mexican War]
Archuleta, Diego
Armijo, Manuel
Magoffin, James Wiley

Stockton, Robert Field
Doniphan, Alexander W.
Carson, Kit
Gillespie, Archibald H.

On June 30, 1846, the Army of the West started for Santa Fe, following the Santa Fe Trail for eight hundred miles. The trail took them first to Bent’s Fort on the Arkansas River and then southward into New Mexico. On the outskirts of Santa Fe, Kearny learned that three thousand Mexicans under the command of Manuel Armijo, the governor of New Mexico, had occupied a strategic canyon through which Kearny’s men would have to pass.

Rather than risk a military clash, Kearny resorted to diplomacy, sending forward intelligence agent James Wiley Magoffin, Magoffin, James Wiley who, acting on secret instructions from Polk Polk, James K.
[p]Polk, James K.;and Mexican War[Mexican War] , succeeded in convincing Armijo Armijo, Manuel that he should flee southward. Colonel Diego Archuleta, Archuleta, Diego Armijo’s second-in-command, proved more difficult and would not withdraw the Mexican army until Kearny promised that he would occupy only part of New Mexico, leaving the rest to Archuleta. Kearny’s army then marched into Santa Fe without contest.

Disregarding his promise to Archuleta, Kearny issued a proclamation announcing the intention of the United States to annex the whole of New Mexico. He promised the residents a democratic government and a code of law, and he named Charles Bent Bent, Charles governor. When settlers in southern New Mexico questioned his actions, Kearny took a detachment down the Rio Grande to ensure the loyalty of Mexican villages.

With the first phase of his campaign completed, Kearny continued his program by separating his army into three forces. One force he left behind in New Mexico to hold the province. Another force, composed of three hundred volunteers from Missouri under Colonel Alexander W. Doniphan, Doniphan, Alexander W. went south by way of El Paso to occupy Chihuahua City. Magoffin, Magoffin, James Wiley sent ahead to ensure a peaceful occupation, was unsuccessful. Doniphan’s troops had to fight the Battle of Brazito before occupying El Paso, and they had to drive back a Mexican army of four thousand at Chihuahua City.

Kearny, meanwhile, had taken the third force of three hundred dragoons out of Santa Fe on September 25, 1846, and headed for California. He was accompanied by Lieutenant William H. Emory Emory, William H. and other officers of the Topographical Engineers, who were making observations on the feasibility of wagon and railroad routes. The expedition moved rapidly down the Rio Grande and then west along the Rio Gila, where it encountered a detachment led by Kit Carson Carson, Kit . Carson brought news that California was in the hands of the United States. Assuming that a military campaign would be unnecessary on the coast, Kearny ordered two-thirds of his troops back to Santa Fe and commanded the reluctant Carson, now a lieutenant in the U.S. Army, to guide him and one hundred dragoons westward.

Kit Carson.

(Library of Congress)

The division of Kearny’s force proved fortunate for the interests of the United States, because the detachment returning to New Mexico arrived in time to suppress the Taos Taos Rebellion (1847) Rebellion led by the disgruntled Archuleta, Archuleta, Diego in which Governor Bent Bent, Charles and other officials had been slain. The revolutionaries took refuge within the adobe church there, and the U.S. forces had to storm the walls and kill many Mexican leaders before the revolt came to an end and U.S. authority was restored.

At the same time, the United States extended its authority to California. Before war had been declared between the United States and Mexico, Thomas O. Larkin, the U.S. consul in California, had hoped that he could effect a peaceful transfer of the Mexican province to the United States. Larkin’s hopes were dashed, however, by events surrounding John C. Frémont’s appearance in California between December, 1845, and June, 1846.

Frémont had secured permission from Governor José Castro (1810-1860) Castro, José for his scientific expedition to winter in California on the condition that Frémont avoid coming near any settlements. Frémont’s failure to honor the agreement prompted Castro to demand Frémont’s departure from California. Avoiding hostilities temporarily, Frémont led his detachment slowly up the Sacramento River Valley, until he was overtaken at Klamath Lake by Lieutenant Archibald H. Gillespie Gillespie, Archibald H. of the U.S. Marines. Gillespie was carrying confidential messages and papers from the U.S. government and from relatives.

The exact contents of these communications have remained unknown; however, after his encounter with Gillespie, Frémont returned to California, despite Castro’s order to leave, and made his way to the vicinity of Sonoma. There, in June, he immediately became involved in an uprising of settlers from the United States known as the Bear Flag Revolt Bear Flag Revolt (1846) . The insurrection takes its name from a flag bearing the symbols of a red star and a bear, which the insurgents led by William B. Ide (1796-1852) Ide, William B. adopted as their standard.

Frémont’s national reputation as a hero in the conquest of California waned when the Bear Flag Revolt was assessed against the efforts of Larkin to secure California peacefully for the United States, and when it was learned that the war with Mexico—which prescribed the U.S. conquest of California—had been declared before the Bear Flag Revolt took place. Critics have censured Frémont for having provocatively endangered relations between the United States and Mexico at a time when Frémont could not have known of the state of war. Historians point out that the Bear Flag Revolt had little importance in the U.S. conquest of California, because Commodore John Sloat’s first official act of conquest was to sail into Monterey Bay and raise the United States flag over the customs house on July 7, twelve days before Frémont’s arrival in Monterey.

Events of the Bear Flag Revolt Bear Flag Revolt (1846) merged with the conquest of California by United States forces. The first stage of operations, from July 7 to August 15, 1846, resulted in the temporary occupation of every important settlement in California, including San Francisco, Sutter’s Fort, Monterey, and Los Angeles Los Angeles;and Bear Flag Revolt[Bear Flag Revolt] . It was news of this success that Kit Carson Carson, Kit was carrying to the east when he met Kearny. Scarcely had Carson departed, however, when a local revolt erupted in Los Angeles on September 22, and the United States troops under Gillespie Gillespie, Archibald H. were forced to retreat to the Pacific port of San Pedro, leaving southern California once again in Mexican hands.

Territorial Growth of the United States

About that time, Commodore Robert Field Stockton Stockton, Robert Field , in charge of U.S. naval forces, left Monterey for the south. Meanwhile, the Mexicans, learning of Kearny’s approach to San Diego, had come out to meet him near present-day Escondido, California. In the ensuing Battle of San Pasqual, United States troops were mauled badly but managed to struggle on to San Diego. Kearny then joined Stockton’s forces in a successful march into Los Angeles. Frémont, in the meantime, marched deliberately down the California coast. The Mexican leaders who had violated their paroles—made at the time of the first capitulation—were afraid of retribution at the hands of Kearny or Stockton, so they sought out Frémont in the mountains north of Los Angeles, where they surrendered at Cahuenga on January 13, 1847. The conquest of the Southwest was at last complete. A bitter quarrel ensued between Stockton and Kearny over who was in command in California. Frémont sided with Stockton Stockton, Robert Field , but Kearny appealed to Washington, D.C., and received confirmation of his authority.


The American Southwest was now de facto in the hands of the United States. Diplomatic complications delayed the signing of the Treaty of Guadalupe Hidalgo until February, 1848, however, more than a year after the fighting in the northern Mexican provinces had ceased. As a result of the treaty, when it was finally signed, the United States acquired all or portions of the future states of California, Nevada, Utah, Colorado, New Mexico, and Arizona. All Native Americans and Mexicans living in those territories passed under the suzerainty of the United States. In addition to the long-term significance of this acquisition, the short-term significance of California’s annexation became apparent almost immediately, as gold had been discovered at John Augustus Sutter’s mill on the American River even before the treaty was signed.

Further Reading

  • Chaffin, Tom. Pathfinder: John Charles Frémont and the Course of American Empire. New York: Hill & Wang, 2002. Well-written, comprehensive, and balanced biography, describing Frémont’s varied life and career. Includes information on his expeditions, relationships with allies and adversaries, and his marriage to Jessie Benton Frémont.
  • Clarke, Dwight L. Stephen Watts Kearny: Soldier of the West. Norman: University of Oklahoma Press, 1961. The definitive biography of Kearny, a leading figure in the conquest of the Southwest.
  • Eisenhower, John S. D. So Far from God: The U.S. War with Mexico, 1846-1848. New York: Random House, 1989. A survey of the Mexican War written for a popular audience.
  • Harlow, Neal. California Conquered: The Annexation of a Mexican Province, 1846-1850. Berkeley: University of California Press, 1982. A thorough treatment of the economic, cultural, and physical conquest of California.
  • Limerick, Patricia Nelson. The Legacy of Conquest: The Unbroken Past of the American West. New York: W. W. Norton, 1987. Argues that the conquest of land by the United States catalyzed social and economic interaction and fashioned the agenda for ongoing problems between subjugated peoples and the majority society.
  • Mahin, Dean B. Olive Branch and Sword: The United States and Mexico, 1845-1848. Jefferson, N.C.: McFarland, 1997. Diplomatic history of the Mexican War that concentrates on the policies of the Polk administration.
  • Roberts, David. A Newer World: Kit Carson, John C. Frémont, and the Claiming of the American West. New York: Simon & Schuster, 2000. An account of Frémont’s expeditions in the Western United States from the early 1840’s until the beginning of the Civil War. Describes Carson’s role in the expeditions and the relationship of the two men.
  • Weber, David J. The Mexican Frontier, 1821-1846: The American Southwest Under Mexico. Albuquerque: University of New Mexico Press, 1982. An outstanding survey of the social, economic, and diplomatic realities of the old Mexican Cession and California.

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Mexican War (1846-1848);postwar settlement
Kearny, Stephen Watts
Frémont, John C.
[p]Frémont, John C.;and California[California]