Date: From 1846-04-25 to 1848-03-10
Caused by tensions resulting from the annexation of Texas, Mexican political instability, and American expansionism, the Mexican War proved to be a highly successful military effort by the United States and resulted in significant territorial gains. The immediate cause was a dispute over Texas's southern border (the United States asserted that it was the Rio Grande River while the Mexicans argued for the Nueces). The dispute escalated to violence following Zachary Taylor's occupation of the disputed region on January 13, 1846, and subsequent attack by Mexican forces on April 25. The ensuing conflict involved three major campaigns: one by Zachary Taylor into northern Mexico resulting in his victories over Antonio Lopez de Santa Anna's forces at Palo Alto, Resaca de la Palma, and Buena Vista; another led by Stephen W. Kearny into New Mexico and California; and a third under Winfield Scott which began with his capture of Vera Cruz and concluded with victories over Santa Anna at Cerro Gordo, Contreras, Chapultepec and capture of Mexico City. The war was concluded by the Treaty of Guadalupe-Hidalgo on March 10, 1848, which ceded most of the current American southwest to the United States.
Domestically, the war was controversial. Democrats, led by President James K. Polk, supported it as part of the broader push for American expansion, known popularly as Manifest Destiny. Many Whigs, particularly in the North, considered the war unjustified and some suspected it was designed primarily to expand the number of slaveholding states. Abraham Lincoln was among the most vocal opponents of the war and famously issued his Spot Resolutions to question its causes and conduct.
Amy S. Greenberg, A Wicked War: Polk, Clay, Lincoln, and the 1846 U.S. Invasion of Mexico (New York: Alfred A. Knopf, 2012); Timothy J. Henderson, A Glorious Defeat: Mexico and its War with the United States (New York: Hill and Wang, 2008); Robert W. Johannsen, To the Halls of the Montezumas: The Mexican War in the American Imagination (New York: Oxford University Press, 1985).