The presidial system was the focus for Spanish and Mexican military operations in northern New Spain. The Spanish established these garrisons to provide their settlers and missionaries protection from hostile indigenous tribes opposing expansion into their territories. Between 1692 and 1776, presidios were established on the Sonoran frontier at Fronteras, Terrenate, Horcasitas, Santa Cruz, Altar, Tubac, Bavispe, Bacoachi, and Tucson. The Spanish and Mexican governments never completely solved the problem of adequately supplying the Sonoran presidios with men and materials to achieve dominance over the native populations. These conditions left the presidios and civilian population exposed to attack and harrassment by hostile Indians. Examination of the major events concerning the presidios from 1790 to 1835, including the Apache pacification policies, establishment of "Indian" presidios, the Mexican war for independence, transfer from Spanish to Mexican control, and the study of presidial personnel, reveals how the presidio functioned as a major frontier institution.