On August 22, 1848, the United States annexed New Mexico. An excerpt from the article:
"On this day in 1846, Gen. Stephen Kearny (1794-1848) established the Territory of New Mexico as a U.S. possession. His proclamation guaranteed freedom of religion and protection for private property in the newly claimed lands.
After fighting erupted in Texas, Congress declared war against Mexico on May 11. At the outbreak of the war, President James Polk named Kearny commander of the Army of the West and ordered him to lead an expeditionary force to occupy New Mexico and California.
Kearny marched to Santa Fe, N.M., without opposition at the head of a force of 1,700 men. His overall forces in the war zone consisted of two regiments of Missouri volunteers, a regiment of New York volunteers who had arrived in California by ship, several artillery and infantry battalions, the First Dragoon Regiment, which Kearny had organized and which served as the genesis of the U.S. cavalry, and the Mormon Battalion. After quickly taking control of much of the area that comprises modern-day New Mexico, Kearny was named as its military governor on Aug. 18. Within another month, he ensured that a civilian government was in place.
When Kearny returned to Washington, he was greeted as a hero. Polk named him governor of Veracruz, and later of Mexico City. He also received a brevet promotion to major general in 1848, over the opposition of Sen. Thomas Hart Benton of Missouri, the father-in-law of Kearny’s wartime rival, Lt. Col. John Fremont. Kearny contracted malaria in Veracruz and returned to St. Louis, where he died at the age of 54. His wife -- the stepdaughter of William Clark of the Lewis and Clark Expedition -- received $30 a month from the government until her death at the age of 88.
The Mexican War marked the coming of the Anglo-American culture to New Mexico, which survives to this day."