The only Thomas Diegnan that I can think of wrote one of a series of books about immigrants coming to American.  His book was called IRISH AMERICANS, and he wrote about their experiences when they came to this country seeking a better way of life.  Many came after a terrible famine has spread across Ireland.  Some came to escape from religious intolerance because they were Catholics, and in the 1820’s some came to help build the Erie Canal.  Most of the immigrants came here between 1820 and 1860 for the reasons that I just mentioned, and probably many more.  They settled in the large cities like Boston, New York and Philadelphia.  They enlisted to help fight the Civil War and won their place in this country by their loyalty and sacrifice, just like any other citizen.