The tune, “March to Battle” is from The Chieftains’ 2010 album, San Patricio.   It’s one of the tunes we will be performing with The Chieftains in Lincoln.  The Saint Patrick's Battalion (Spanish: Batallón de San Patricio), formed and led by John Riley, was a unit of 175 to several hundred immigrants (accounts vary) and expatriates of European descent who fought as part of the Mexican Army against the United States in the Mexican–American War of 1846-8. Most of the battalion's members had deserted or defected from the United States Army.

John Patrick Riley (Irish: Seán Pádraic Ó Raghallaigh), also known as John Patrick O'Riley, (c. 1817 – August 1850), was born in Clifden, County Galway, Ireland.  Riley served with the British Army before immigrating to Canada. Connemara and other rural regions suffered greatly during the Great Famine, and millions of people emigrated by ship from Ireland to Canada and the United States to survive.

Soon after his arrival in the United States in Michigan, Riley enlisted in the US Army. Many immigrants were recruited in the 1840s; some served just to earn some money, as they had usually fled famine and severe poverty in their home countries.

Prior to his desertion, Riley served in Company K of the 5th US Infantry Regiment. Riley and Patrick Dalton formed the Batallón de San Patricio, or the Saint Patrick's Battalion. Composed primarily of Catholic Irish and German immigrants, the battalion also included Canadians, English, French, Italians, Poles, Scots, Spaniards, Swiss, and Mexican people, most of whom were members of the Catholic Church. Disenfranchised Americans were in the ranks, including escaped slaves from the Southern United States. The Mexican government offered incentives to foreigners who would enlist in its army: granting them citizenship, paying higher wages than the U.S. Army and the offer of generous land grants. Only a few members of the Saint Patrick's Battalion were actual U.S. citizens.

Members of the Battalion are known to have deserted from U.S. Army regiments including: the 1st Artillery, the 2nd Artillery, the 3rd Artillery, the 4th Artillery, the 2nd Dragoons, the 2nd Infantry, the 3rd Infantry, the 4th Infantry, the 5th Infantry, the 6th Infantry, the 7th Infantry and the 8th Infantry.  The Battalion served as an artillery unit for much of the war. Despite later being formally designated as infantry, it still retained artillery pieces throughout the conflict. In many ways, the battalion acted as the sole Mexican counter-balance to U.S. horse artillery.

They fought at several battles and finally at the Battle of Churubusco, on the outskirts of Mexico City, where more than 70 were captured by US forces and the rest disbanded. Men of the disbanded battalion went on to fight at the Battle for Mexico City.

For Americans of the generation that fought the Mexican-American War, the San Patricios were considered traitors. For Mexicans of that generation, and generations to come, the San Patricios were heroes who came to the aid of fellow Catholics in need.

Because Riley had deserted before the US declared war against Mexico, he was not sentenced to execution following his conviction at the court martial held in Mexico City in 1847. He testified to deserting because of discrimination against and mistreatment of Irish Catholics in the US Army, and anti-Catholicism which he had encountered in the United States. While escaping the mass hanging of about 50 other captured members of the Saint Patrick's Battalion, Riley was branded on his cheek with the letter "D" for deserter.

Following his conviction and branding, Riley was released and eventually rejoined the Mexican forces. Reportedly he grew his hair to conceal the scars on his face. He continued to serve with the regular Mexican Army after the end of the war, being confirmed in the rank of "Permanent Major". Stationed in Veracruz, he was retired on August 14 1850 on medical grounds after suffering from yellow fever.