The Mexican Frontier, 1821–1846 published by other historians. This work was supplemented by additional primary materials which he discovered in the archives that allowed him to delve further into certain areas. "The Mexican Frontier" examines the southwestern United States, specifically the areas now known as Arizona, California, New Mexico, and Texas, in the twenty-five years between Mexico's independence from Spain and the beginning of the Mexican–American War. This resulted in the transfer of control of the border areas to the United States. In the early days of the Republic of Mexico, these areas comprised its northern border, including the territories of Alta California and
Antonio López de Santa Anna enough to send him to school. In June 1810, the 16-year-old Santa Anna joined the Fijo de Veracruz infantry regiment as a cadet against the wishes of his parents, who wanted him to pursue a career in commerce. In September 1810, secular cleric Miguel Hidalgo y Costilla rebelled against Spanish rule, sparking a spontaneous mass movement in Mexico's rich agricultural area, the Bajío. The Mexican War of Independence was to last until 1821, and Santa Anna, like most creole military men, fought for the crown against the mixed-raced insurgents for independence. Santa Anna's commanding officer was José Joaquín de Arredondo,