In the 1840s political boundaries were shifting in the west. With the conclusion of the Mexican-American War, Mexico Mexico ceded approximately 55 percent (525,000 square miles) of its territory, including the present-day states California, Nevada, Utah, New Mexico, most of Arizona and Colorado, and parts of Oklahoma, Kansas, and Wyoming to the U.S. With the
Treaty of Guadalupe Hidalgo, much of the southwest was organized into the New Mexico Territory. It would take some time to establish boundaries for the states as they are currently known.
States and Territories, 1850