It's a very loose rendition of the generic Gaelic "aisling" tradition addressing Ireland as "Kathleen" or "Kathleen Ni Houlihan". As the personified sovereignty-goddess she was supposed to be the spouse of the land's king. The poem enumerates her earlier spouses or High Kings: Conn stands for Connacht, Niall for Ulster, Brian for Munster, Rory for Leinster. But now (after the English conquest) she has no true spouse, and the poet bitterly confronts Ireland's/Kathleen's lost honour and esteem, like an aging prostitute.
I think it's a brilliant modernization of the 18th-century model, very concise and terse but pregnant with emotion and meaning, and with all the mixed feeling of compassion and bitterness.