William Walker (1824-60), an American adventurer living in California, was involved in a scheme to establish American settlements in Mexico. He organized a filibustering expedition and, on the pretext of protecting mexicans from the Apache Indians rampaging in northwestern Mexico, sailed from San Franciso on October 15, 1853. With his armed force, Walker landed at La Paz in Baja or Lower California, which he proclaimed an independent republic with himself as president (November 3, 1853). He then announced the annexation of the Mexican state of Sonora (January 18, 1854). The Mexicans frequently attacked the American invaders, who were forced to flee from Mexico because of a lack of provisions and ammunition. In May 1854, Walker surrendered to US authorities at the border near San Diego. Soon tried for violating neutrality laws, he was acquitted and, about a year later, resumed his filibustering activities in Nicaragua.