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John O’Neill (born March 8, 1834, County Monaghan, Ire.—died Jan. 7, 1878, Omaha, Neb., U.S.) was an Irish-born military leader of the American branch of the Fenians, an Irish nationalist secret society. O’Neill immigrated to the United States at the age of 14 to join his mother and older siblings at their home in Elizabeth, N.J. He attended school for a year and then held a number of jobs. After serving as a Union cavalry...