William Walker captures La Paz and declares the Republic of Sonora

Background. In the summer of 1853, William Walker traveled to Guaymas seeking a grant from the government of Mexico to create a colony that would serve as a fortified frontier, protecting US soil from raids by Native Americans. Motivated by an earlier filibustering project of Gaston de Raousset-Boulbon, he attempted in 1853–54 to take Baja California and Sonora. On October 15, 1853, Walker set out with forty-five men to conquer the Mexican territories of Baja California and Sonora.

Proclamation of the Republic. Walker succeeded in capturing La Paz, the capital of sparsely populated Baja California. On November 3, 1853, he declared La Paz the capital of a new "Republic of Lower California," with himself as president. The Republic of Baja California and Sonora, simply known as the Republic of Sonora, was a short-lived, unrecognized federal republic ruled by Walker in 1854.

Legal Framework. Walker placed the region under the laws of the American state of Louisiana, where slavery remained legal in 1854. In November 1853, he stated that the civil code and procedures of Louisiana would be followed for government and law until the courts of the republic were organized. This legal structure defined the governance of his short-lived republic.