The singer was born in America. His "pack is all over American earth. My blood is as Irish as Irish can be." He is ashamed that the "tyrants" control "our poor plundered Ireland." He waits for the summons to return to Ireland with his rifle.
It is a curiosity that, in the late nineteenth century, the Irish in America were often more militant in favor of liberty than the Irish still at home. (Look at how many of the Fenian exploits were organized in America.) One can only speculate at the reasons: The Irish in America were not experiencing the slow liberalization that occurred in Ireland, they had more money and didn't have to scrabble as hard for a living -- and, of course, their ancestors included most of the worst troublemakers who simply could not stomach British rule.
For an example of such, see the notes to "Erin's Lovely Lee."
The Fenians would eventually plan an invasion of Ireland; as usual, nothing much came of it. - RBW