Page "Southwestern United States" Paragraph 4

Most of it was a part of the Viceroyalty of New Spain, in the Spanish Empire, during the Modern Era.

California, Arizona, Nevada, Utah, and parts of New Mexico, Colorado, Wyoming, Oklahoma and Kansas were originally all part of Mexico before the Mexican-American War.

Portions of some of the areas in the " divided " states, and including western parts of Texas, were those in dispute after the Texas Revolution.