During the Civil War the Irish were represented well on both sides.
The Union Irish Brigade was made up of the 69th NY, 63rd NY, 88th NY, 116th Penn, and 28th Mass. Many of these men were fresh off the boats from the old country. The original and best known Regiment was the 69th known as the Fighting 69th.
After the war some of the Chaplains of the Brigade were on the staff at Notre Dame. It is said that from them the University adopted the name "Fighting Irish"