As the Civil War began, the newly arrived immigrant population of New York City showed tremendous patriotism. Recruiting posters in Irish neighborhoods encouraged men to enlist, and several New York regiments were made up almost entirely of Irish immigrants.
When the 69th New York Regiment left New York to join the US Army in Virginia in 1861 a huge parade marched past the old St. Patrick's Cathedral on Mott Street. This popular lithograph shows the exuberance the Irish in New York felt toward the war effort.
Of course, in 1861 most Americans anticipated that the uprising in the south would be put down fairly quickly.