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
Solemn Act of the Declaration of Independence of Northern America Solemn Act of the Declaration of Independence of Northern America The Solemn Act of Northern America's Declaration of Independence () is the first Mexican legal historical document which established the separation of Mexico from Spanish rule. It was signed on November 6, 1813, by the deputies of the Congress of Anáhuac, organized by General José María Morelos in the city of Oaxaca in June of that same year, and later installed in the city of Chilpancingo on September 13. The document gathers some of the main political uprisings contained in "Feelings of the Nation" ("Sentimientos de la Nación"), a document