In the mid-19th century, large numbers of Irish immigrants were conscripted into Irish regiments of the United States Army at the time of the Mexican–American War. The vast majority of the 4,811 Irish-born soldiers served in the U.S. Army, but some deserted to the Mexican Army, primarily to escape mistreatment by Protestant officers and the strong anti-Catholic discrimination in America. These were the "San Patricios", or Saint Patrick's Battalion—a group of Irish led by Galway-born John O'Riley, with some German, Scottish and American Catholics. They fought until their surrender at the decisive Battle of Churubusco, and were executed outside Mexico City by the American government on 13 September 1847. The battalion is commemorated in Mexico each year on 12 September.