Chiming in a bit late, perhaps, but it seems to me that the song pleads for unification of the whole island ("North men, South men" and "Dublin, Belfast, Cork, and Donegal" pull in all 4 traditional provinces) as well as a wish for independence ("A Nation Once Again" is another fine song). The United Irishmen fought together (Protestants and Catholics) against the British in the rising of 1798. And I agree that it is not obscure and definitely not the national anthem of the Republic.