Santa Fe seceded from Mexico in 1836 and the Republic of Texas claimed it as part of the western part of Texas, falling along the Rio Grande. A military and trading expedition in 1841 left Austin, Texas and made its way to Santa Fe to gain control over the entire trail. The force was not executed properly and was captured by the Army from Mexico. In 1846, the U.S. declared war on Mexico and 1700 soldiers were led into Santa Fe by Brigadier General Stephen W. Kearny. They claimed the city and the entire New Mexico territory for the United States. By the year 1848, the United States gained New Mexico officially during the Treaty of Guadalupe Hidalgo.
Once New Mexico became a state, support was minimal. One traveler commented on how the people looked poor and that the entire surrounding country was barren.
Jean Baptiste Lamy arrived in 1851 and he became the bishop of Arizona, Utah, New Mexico and Colorado in 1853. He traveled extensively in Europe and the United States and helped to establish Catholicism in the region.
In 1862, the Confederate flag flew over Santa Fe for a few days in March until General Henry Sibley was defeated by union troops