Territory Ceded by México Under the Treaty of Guadalupe Hidalgo in 1848 and the Gadsden Purchase of 1853.
When Texas was officially recognized as a state in 1845, it included the light-gray area, which was also claimed by México. The Treaty of Guadalupe Hidalgo resolved this dispute, with Texas claiming the disputed land. In 1850, Texas transferred part of this land to the federal government, which became the eastern portion of the territory of New Mexico.