Page "Colorado Territory" Paragraph 3

The land which ultimately became the Colorado Territory had first come under the jurisdiction of the United States in three stages: the 1803 Louisiana Purchase as adjusted by the 1819 Adams-Onis Treaty, the 1845 Annexation of Texas, and the 1848 Mexican Cession.

The land claims of Texas were, at first, controversial.

The border between the USA and Mexico was redefined by the Treaty of Guadalupe Hidalgo at the end of the Mexican-American War in 1848, and the final boundaries of the state of Texas were established by the Congressional Compromise of 1850.