Short answers, pulled from the story.
An estimated 150,000 Irish-Americans fought for the Union during the Civil War. Seven Union generals were Irish-born, and Irish-Americans served as officers, volunteers, and draftees throughout the conflict.
The two first recorded combat deaths in the Civil War were both Irish-born men. Danial Hough, from Tipperary, and Edward Galloway, from Cork, were mortally wounded at Fort Sumter in April 1861 when a magazine exploded during the Union's withdrawal ceremony. Hough died shortly after the explosion; Galloway died five days later.
Irish immigrants rioted because the Enrollment Act of the 3rd of March 1863 made them liable for the draft after they had accepted U.S. citizenship, a consequence many had not anticipated. They were further angered that Black men were excluded from the same draft while wealthy men could avoid service by paying $300 or hiring a substitute. An estimated 120 people died in the New York City draft riots of July 1863, making them the deadliest civil insurrection in American history.
The Davis Guard, a company of mostly Irish-American men from the Houston and Galveston area, received the only physical medals awarded by the Confederacy after winning a decisive victory at the Second Battle of Sabine Pass in 1863. The medals were made from polished Mexican silver coins and hung from green ribbons to honor the soldiers' Irish heritage.
A significant number of Irish-American veterans used their military experience to pursue Irish independence. As members of the Irish Republican Brotherhood, the Fenian Brotherhood, and Clan na Gael, they organized the Fenian Rising in British Ireland and the Fenian Raids into Canada, aiming to establish an independent Irish Republic.
The Irish Brigade was formed after the First Battle of Bull Run, incorporating the 69th New York Infantry. At the Battle of Fredericksburg in 1862, the brigade charged up Marye's Heights and suffered 41.4% casualties. Before facing Pickett's Charge at Gettysburg in 1863, the brigade held a Catholic mass.