The Southwestern United States is a region defined in different ways by different sources. Broad definitions include nearly a quarter of the United States, including Arizona, California, Colorado, Nevada, New Mexico, Oklahoma, Texas and Utah. Narrowly defined, the "core" Southwest might include only Arizona and New Mexico, with parts of the other states making up the beginnings and endings of the Southwest. The five main southwestern states of Arizona, New Mexico, Colorado, Utah, and Nevada are also all considered part of the Mountain West, as well as the southwest. The total population of these states are roughly 19 million people.
Most of it was a part of the Viceroyalty of New Spain, in the Spanish Empire, during the Modern Era.