The San Patricios

The Elite "fightin' Irish" who fought for the Mexican side in the Mexican-American War

The San Patricios: the elite “fightin’ Irish” who fought for the Mexican side in the Mexican-American War

By Sheryl Losser

The Mexican-American War: Attack on Chapultepec Castle, print by Nathaniel Currier, 1848 (Library of Congress, Washington,D.C.)

The St. Patrick’s Battalion – known in Mexico as the San Patricios -- was a group of Irishmen who defected from the U.S. Army to fight for the Mexican side of the Mexican-American War.  Known for their bravery and valor, the men—most, but not all, Irish – fought with distinction and are honored today in both Mexico and Ireland.

John Riley becomes the first to desert the US Army

John Riley was born in Galway County, Ireland between 1805 and 1818.  At the time, Ireland was a poor country and hit hard even before the great famine of 1845.  Riley made his way to Canada and eventually to Michigan in the United States.  He was an excellent artilleryman and joined the U.S. Army where he was stationed at Fort Mackinac to train West Point cadets.

Riley became very disillusioned with the United States.  There was a lot of anti-immigrant and anti-Catholic sentiment, there was talk of Western expansionism and going to war with Mexico, and the immigrants in the army were treated very harshly. He was eventually sent to Texas where he promptly deserted the U.S. Army on April 12, 1846, slipping across the border to Mexico and offering his services to the Mexican army. 

James K. Polk and Manifest Destiny

President James K. Polk believed in Manifest Destiny, an ideology that embraced the idea that white Americans were divinely ordained to settle the entire continent of North America from the Atlantic Ocean to the Pacific Ocean.  Not all Americans, especially Northerners and Irish immigrants, agreed with Manifest Destiny, and they did not want a war with Mexico.  Many felt that his plans were merely an attempt to expand U.S. territory to increase the number of slave states.

Abraham Lincoln Photo by Library of Congress on Unsplash

When Polk sent troops to the disputed territory in Texas, his critics became more outspoken believing this would lead to war with Mexico.  Then-Congressman Abraham Lincoln argued that “President James Polk sent American military forces into the disputed territory to intentionally provoke a military response from Mexico who was just defending their homeland from an invasion.”

Polk’s provocative action did lead to the Mexican-American War and ultimately led to the U.S. Civil War.