The Chieftains are an Irish musical group founded in 1962, who are best known for being one of the first bands to make Irish traditional music popular around the world. Their 2010 album San Patricio is a tribute to the San Patricios, a unit of mostly Irish soldiers, who deserted or defected from the US army to fight with the Mexicans against the United States in the Mexican-American War of 1846 to 1848. This song tells of the battalion crossing the American/Mexican border at the Rio Grande.
Chieftains' leader Paddy Moloney told Billboard magazine where the idea for the album came from: "It took me two years to make the album, but the connection goes back a long way. I started thinking about this 30 years ago. I had a good friend of mine form Trinity College in Dublin. He was doing a lot of research on the American Civil War and all the Irish that fought the war. And this man, John Riley, he was drafted the minute he got off the plank and told to join the Union Army. And one of the things he wasn't too happy about was having to go shoot Catholic Mexicans. And he also saw the injustice of the whole war. And we had the same situation back in Ireland. With the neighbors who came to visit and forgot to go back. So, it was a different face, different region, but similar story."
Moloney's original approach was to write a symphony about what happened and this march is the nearest thing on the album to his initial plan. However, he explained, "I kept adding and adding to it and in the end over eight people were in that song, including Liam Neeson, who did the narration.But the regional Mexican music, my whole feeling for this album changed after I got into it. I did Lila Downs first, and then got to hear more. And when I went there [to Mexico] I was introduced to other musicians I hadn't intended to record. And to hear these instruments, and the tunes they were playing, for God's sake. They go back to the 19th century."
Moloney explained why the album was recorded mainly in Spanish: "It's the first time I did an album almost entirely in another language. For me, language is one thing, but I go for the music. We've mixed Irish music with Chinese music [in the past]. I think this is a much more complete album where the Spanish has taken over. I'm a melody person and I love the structure, and I thought there was no problem whatsoever to blend it and make a fusion of our music with the Mexican music."