Religion, Anti-Catholicism, and the Mexican-American War
Authors: Pinheiro John C. 
Published: October 2017

The death and carnage that accompany war usually lead participants to seek transcendent meaning in their suffering as well as in their defeat or victory. This was especially true of the Mexican War, a conflict that deeply affected the growth of civil religion in the United States even as it tested the limits of religious pluralism. Religion gave Americans the most effective means of making sense out of their conflict with Mexico, even as it helped them solidify a national identity as a providentially blessed republic of Anglo-Saxon Protestants.

The Mexican-American War of 1846–1848 was tremendously consequential for both countries. Its immediate cause lay in a dispute over territory claimed by both countries along the border of the newly annexed American state of Texas. Mexican and American troops clashed there on April 25, 1846. The U.S. Congress, though not without some grumbling, quickly responded to a request by President James K. Polk and declared war on Mexico.

In the war, the U.S. Army invaded Mexico by land and sea, taking the capital on September 14, 1847. Other than a few skirmishes and scattered guerrilla attacks, the fighting war was over. In the Treaty of Guadalupe Hidalgo ending the conflict, Mexico ceded nearly its entire northern frontier—one-third of its territory—to the United States.

The war occurred on the heels of the Second Great Awakening and amid the westward migration of the new, much-persecuted Church of Jesus Christ of Latter-Day Saints, or Mormons. At the same time, heavy Irish immigration had reawakened a latent anti-Catholicism, resulting in new political parties, fights over religion in public schools, and deadly anti-Catholic rioting. While evangelical Protestants got to work refining a civil-religious discourse that depended for its intelligibility on anti-Catholicism, nativist politicians began adopting Christian terminology. Thus, the war between the overwhelmingly Protestant United States and Catholic Mexico became the means by which anti-Catholicism emerged as integral to American identity and American belief in a God-given, special mission to the world: spreading liberty and republican government, along with their prerequisite, Protestant Christianity.

Religion impacted the war in other important ways. The U.S. Army sponsored the Mormon Battalion, the only regular U.S. Army unit ever organized along religious lines. Religion also played a role in the formation by American deserters of the Mexican army brigade known as the San Patricios. And despite U.S. government policy to the contrary, a few U.S. soldiers, inspired by recruiters and derogatory descriptions of Mexican religion by American writers and preachers, vandalized and robbed Mexican churches and committed other atrocities. Meanwhile, the war challenged Protestant pacifists and abolitionists, who wondered whether an otherwise evil war could produce the good fruit of opening Mexico to Protestant missionaries or excising Catholicism from the continent.

As a result of the brief but far-reaching Mexican-American War, Americans now possessed a civil religious sentiment and common identity that was intelligible only within a Protestant milieu and through a distinctively American anti-Catholic discourse.