St. Patrick’s Day: The Unknown Story of the San Patricios Battalion During the Mexican-American War

This article was originally published on March 17, 2022.

When you think of St. Patrick’s Day in the U.S., you probably think of Guinness beer, corned beef, and cabbage. But in Mexico, St. Patrick’s Day symbolizes something very different.

In Mexico, St. Patrick’s Day is a day to commemorate the San Patricios battalion in the Mexican-American War — a Mexican army regiment made up of primarily Irish-Catholic immigrants who deserted the U.S. Army to fight for Mexico.

Before celebrating St. Patrick’s Day, let’s refresh our memory

The Mexican-American war was a conflict between the United States and Mexico between 1846 and 1848.

The war began as part of the U.S.’s “manifest destiny” philosophy — the belief that God destined the U.S. to expand across North America. The nation’s goal was to annex a chunk of Mexico’s land — what now makes up eight states in the U.S., including Texas.

The San Patricios Battalion comprised over 200 men, led by Irish-American commander John Riley. The men participated in six known battles, including the crucial Battle of Buena Vista. They faced their final defeat in the battle of Churubusco.

Why did so many Irish decide to change sides?

Historians agree the primary reasons were frustration over the prejudice of being Irish immigrants in the U.S. Army. They also suggest Irish immigrants were angry for being forced to attend Protestant services. Most importantly, there was a general disagreement over how the U.S. was invading and taking over Mexican territory. 

Not only that, but the Mexican government conducted a successful propaganda campaign targeted at Irish-Catholic soldiers. They successfully appealed to the soldiers’ morality, religion, and desire for economic freedom. 

In one pamphlet written by Mexican General Ampudía, he urged U.S. soldiers not to “contribute to defending robbery and usurpation [of Mexican land] which, be assured, the civilized nations of Europe look upon with the utmost indignation.” 

Another Mexican commander offered any U.S. soldier who deserted “320 acres of good land.” According to contemporary sources, Catholic Priests in Mexico were also instrumental in recruiting U.S. soldiers to fight for Mexico. 

Retaliation and consequences

After the San Patricios battalion was defeated at Churubusco, the U.S. military punished the deserters harshly and labeled them traitors. The U.S. military hanged approximately 50 soldiers from the San Patricios, while some were whipped and branded with the letter “D” to label them deserters and sentence them to hard labor. 

Hence, St. Patrick’s Day has a different meaning in Mexico.

Today, both Mexico and Ireland honor the men who risked it all to fight for the side they believed in. In 2003, then-president of Mexico Vicente Fox praised the San Patricios Battalion in a speech, saying that “the affinities between Ireland and Mexico go back to the first years of our nation when our country fought to preserve its national sovereignty… Then, a brave group of Irish soldiers… in a heroic gesture, decided to fight against the foreign ground invasion.” 

In 1997, Mexico and Ireland jointly released a postage stamp to commemorate the bravery of the soldiers of the San Patricios Battalion on the 150th anniversary of the soldiers’ death.

And every year, on March 17, Mexico uses the St. Patrick’s Day holiday to honor the men who bravely fought for their country.