The Mexican Frontier, 1821–1846: The American Southwest Under Mexico by historian David J. Weber is a history of the part of Mexico's north and northwest that became part of the United States after the Mexican–American War. The book examines territories on the northern frontier of Mexico, including what is now Arizona, California, New Mexico, and Texas, in the twenty-five years after Mexico gained its independence from Spain. Weber emphasizes the role of Mexicans in the region through this period of transition, particularly before and during the Texas war of independence, as well as exploring the region as a whole while acknowledging its distinct communities.