More than 150,000 Irishmen, most of whom were recent immigrants and many of whom were not yet U.S. citizens, joined the Union Army during the Civil War. Some joined out of loyalty to their new home. Others hoped that such a conspicuous display of patriotism might put a stop to anti-Irish discrimination. As the war dragged on and Irish casualties mounted, however, their sympathy for the Union cause began to flag, and by the end of the war many had abandoned the Northern cause altogether. But between 1861 and 1863, the soldiers who fought in the all-Irish units that made up the “Irish Brigade” were known for their courage, ferocity and toughness in battle.