Short answers, pulled from the story.
An estimated 150,000 Irish-Americans fought for the Union during the four-year conflict from 1861 to 1865. This figure represents a significant portion of the immigrant population that joined the Northern states loyal to President Abraham Lincoln.
The riots began on the 13th of July 1863 due to anger over the Enrollment Act passed on the 3rd of March 1863 which required single male citizens aged 20 to 45 to register for military service. Black men mostly freed slaves were excluded from this same draft which added fuel to the fire of anger and fear regarding labor competition.
Six Confederate generals were Irish-born including Patrick Cleburne who held the highest ranking position among them. Units such as the Charleston Irish Volunteers attracted Confederate Irish-Americans in South Carolina while the 24th Georgia Volunteer Infantry followed General Thomas Reade Rootes Cobb.
Fort Sumter exploded in April 1861 killing Danial Hough born in Tipperary and Edward Galloway born in Cork as the first recorded combat deaths. These events marked the beginning of significant casualties for Irish immigrants serving in the Union forces.
At the Battle of Fredericksburg in 1862 the brigade charged up Marye's Heights suffering 41.4% casualties. The 69th New York Volunteers flew a green flag with a golden harp symbolizing Ireland alongside normal regimental colors before this engagement.