In the 1800s, parts of what later became western and southern Colorado were claimed by both the Republic of Texas and Mexico.
Texas asserted its borders extended to parts of modern-day New Mexico, Colorado and even Wyoming. The formerly disputed territory includes Aspen, Vail, Crested Butte, Steamboat Springs and Rawlins, Wyoming.
Mexico did not recognize Texas’ claims, leading to border skirmishes that became a justification for the Mexican-American war in 1846. The war ended in 1848 with the Treaty of Guadalupe Hidalgo, in which Mexico agreed to cede 55% of its land to the U.S., or around 525,000 square miles, including parts of what later became Colorado.
The U.S. government purchased Texas’ claims to Colorado in 1850. These lands, combined with territory acquired through the Louisiana Purchase and the Treaty of Guadalupe Hidalgo, became the Colorado Territory in 1861. Colorado became a state in 1876.
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