What new western territories did the United States acquire in the mid-1800s?
The Louisiana Purchase of 1803 brought a huge swath of the West into the United States. 1803, however is not the mid-1800s. Territiories acquired by the United States between 1825 and 1875 include: The United States annexed the Republic of Texas in 1845. This brought in the entirity of present day State of Texas, plus parts of New Mexico, Oklahoma, Kansas, Wyoming, and Colorado. The Oregon Treaty of 1846 gave the United States complete control over Oregon Territiory, the present day states of Washington, Oregon and Idaho, plus parts of Montana and Wyoming. In 1848, after the Mexica-American War, the Treaty of Guadalupe Hidalgo gave the Unted States the psresent day states of California, Nevada and Utah, plus parts of Colorado, Arizona, New Mexico, and Wyoming. The Gadsden Purchase of 1853 gave the United States southern Arizon and part of Southern New Mexico. The United States purchased Alaksa in 1867.
