Matt, I guess it would depend on how far back you wish to go to get context. Anglo-Norman incursions into Ireland began in the 12th century. In addition to the titles TJ mentions above, you might wish to take a look at biographies of some figures like Michael Collins or Eamon de Valera to get historical context. I’m sure there’s at least one good book about the Easter Rising out there, but I am not really up on the bibliography of 20th-century Ireland. I suspect Prof. Casey would know more.