I'd heard from Steve Sailer that Mexicans in general are more likely than Americans to have strong feelings about the Mexican-American War of 1846. I had never been too surprised about this, after all, I live in a state that was part of the spoils of that war. To the extent that I really thought about it at all, I figured that I would be pissed if my side lost too.
However, I read an article by Michael Hogan in Crisis Magazine about Mexico's Irish soldiers. The idea of Europeans fighting in the Mexican army was not particularly surprising, especially given that Ireland and Mexico are both Catholic countries. What I had never heard of was the Irish soldiers from the American army who defected and joined the Mexican army.
The causes of the defections are not difficult to imagine. The war occurred near the pinnacle of anti-Irish sentiment in America. The Bible Riots had taken place in Philadelphia in 1844, and further violence had nearly broken out in New York. Not to mention, at the time the Vatican actually was a foreign power, with its own army. To be fair, the Irish were pretty much the illiterate drunken brawlers popular opinion held them to be. The enterprising efforts of bishops such as Archbishop 'Dagger' John Hughes of New York and Archbishop John Ireland of St. Paul, MN to civilize the Irish and make them good Americans has largely been forgotten by now. However, the improvement had yet to take place, so the Irish were treated poorly by their compatriots in the Army. In addition to this, the anti-Catholicism of the Protestant troops in the Army led to the desecration of Churches in Mexico.
This was too much for some of the Irish to bear, so they defected to the Mexican side, taking their cannons with them. The addition of an Irish artillery battalion to the Mexican Army made the war more even. The Los San Patricos acquitted themselves well in several battles. However, the Mexicans still lost, and those deserters who were captured were flogged and then hanged.
I have some sympathy for the Mexicans on this, I would in fact still be pissed if the beautiful church in which I was married was turned into a stable.