At the outbreak of the Civil War in 1861, thousands of Irish and Irish-American New Yorkers enlisted in the Union Army. Some joined ordinary—that is, non-Irish—regiments, but others formed three all-Irish voluntary infantries: the 63rd New York Infantry Regiment, organized on Staten Island, and the 69th and 88th New York Infantry Regiments, organized in the Bronx. These units would form the core of what would come to be called the Irish Brigade.

Ethnic units were a way for the Union Army to help win Irish support for its cause. This support was not guaranteed: Though most Irish immigrants lived in the North, they were sympathetic to (as they saw it) the Confederacy’s struggle for independence from an overbearing government—it reminded them of their fight to be free of the British. Also, many Irish and Irish Americans were not against slavery. On the contrary, they favored a system that kept blacks out of the paid labor market and away from their jobs. As a result, Union officials had to promise many things in addition to ethnic regiments—enlistment bonuses, extra rations, state subsidies for soldiers’ families, Catholic chaplains—in order to assure that the North’s largest immigrant group would be fighting with them and not against them.

In February 1862, an Army captain named Thomas Francis Meagher became the Brigadier General of the nascent Irish Brigade. Meagher was born in Ireland, where he had been active in the “Young Ireland” nationalist movement and exiled as a result to the British Penal Colony in Tasmania, Australia. He escaped from Australia in 1853 and came to the United States, where he became a well-known orator and activist on behalf of the Irish nationalist cause. He joined the Army early in 1861. Meagher was ambitious, and he knew that if he could raise an all-Irish infantry brigade, Union Army officials would have to make him its commander. He also hoped that an Irish Brigade in the U.S. would draw attention to the nationalist cause at home.

In the spring of 1862, Union Army officials added a non-Irish regiment, the 29th Massachusetts, to the Irish Brigade in order to beef up its numbers before the Peninsula Campaign for the capture of Richmond, Virginia, the capital of the Confederacy. In October, another Irish regiment, the 116th Pennsylvania Infantry Regiment from Philadelphia, joined the brigade in time for the battle at Harper’s Ferry, Virginia. The next month, officials swapped the non-Irish 29th Massachusetts Regiment for the Irish 28th Massachusetts.

Thanks to their toughness and bravery, the five-regiment Irish Brigade led the Union charge in many of the Army of the Potomac’s major battles. This meant that they suffered disproportionate numbers of casualties. At the Battle of Antietam, in September 1862, about 60 percent of the soldiers in the 63rd and 69th New York regiments, almost 600 men in all, were killed in battle. A few months later, at the Battle of Fredericksburg, 545 of the brigade’s 1,200 men were killed or wounded. “Irish blood and Irish bones cover that terrible field today,” wrote one soldier. “We are slaughtered like sheep.”

In July 1863, at the Battle of Gettysburg, about 320 of the Irish Brigade’s remaining 530 soldiers were killed. (There is a monument to the Irish Brigade on the battlefield there: a green malachite Celtic cross with a trefoil, an Irish harp and the numbers of the three New York Irish regiments rendered in bronze on its front. At the cross’s feet lies a statue of an Irish wolfhound, a symbol of steadfastness and honor.)

Many historians say that the Battle of Gettysburg was the Civil War’s turning point toward Union victory. It was also the turning point for the Irish Brigade. By the summer of 1863, the tragically high numbers of casualties in the Brigade led many Irish soldiers and their families to believe that the Union Army was taking advantage of their willingness to fight by using them as cannon fodder. They were further infuriated by the National Conscription Act, passed in March of that year, which made every unmarried man in the Union between the ages of 21 and 45 subject to a draft lottery unless he could hire a replacement or pay a $300 fee. As many working-class Irish people saw it, this was discrimination: They were poor men being forced to fight in a “rich man’s war.” At the same time, many Irish people had come to believe that the government’s reasons for fighting the war had changed: It was not about preserving the Union any longer but about ending slavery—a cause that most Irish people in the U.S. emphatically did not support.

These tensions boiled over in New York City on July 13, about a week after the Battle of Gettysburg, when thousands of Irish immigrants took to the streets for five days in violent protest against the draft law—and, more generally, against the black people they blamed for the war. Mobs assaulted any black person they saw on the street, ransacked and burned homes in African-American neighborhoods, and looted stores owned by blacks and “sympathetic” whites. Federal troops arrived in the city on July 16 to quell the disorder. At least 120 people, most of them African-American, died in the violence.

This outburst of racist violence marked the end of organized Irish participation in the Civil War, though individual Irishmen continued to serve as soldiers in the Union Army. The Irish Brigade diminished greatly in size and disbanded for good in 1864.