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
Spanish conquest of the Aztec Empire "The Aztecs Under Spanish Rule: A History of the Indians of the Valley of Mexico, 1519–1810" (1964) were central in reshaping the historiography of the indigenous and their communities from the Spanish Conquest to the 1810 Mexican independence era. Scholars who were part of a branch of Mesoamerican ethnohistory, more recently called the New Philology have, using indigenous texts in the indigenous languages, been able to examine in considerable detail how the indigenous lived during the era of Spanish colonial rule. A major work that utilizes colonial-era indigenous texts as its main source is James Lockhart's "The Nahuas After the