What really bugged me about this was that The Cardassians had been DROPPED into the Future History of Trek from basically out of nowhere. Not only had we never seen these ugly guys, suddenly O'Brien had this story about Setlik 3 he starts telling.
Apparently "The Cardassian War" had been over for a couple of years, when The Enterprise D first pulled out of The Utopia Plenicia Shipyards. But until this episode we had seen not hide nor hair nor even the spoons in their skulls.
Bob Gunton is Captain Benjamin Maxwell, who had been stuffing some Cardy-related emotions and now he is out of control, he goes into Cardy space and starts blowing up ships and space stations.
So as The D enters Cardy space and Gul Macet (Marc Alaimo) starts shooting at them, Picard is handed a worm can that he has to fix.
But in Maxwell's Mind, he is not doing anything wrong. In fact, the Cardassian War never ended for him.
The problem is, Maxwell is right, but he's going about it the wrong way. How do we deal with a guy named Maxwell? We need a guy named O'Brien. But before O'Brien can help Maxwell, he has to face his own prejudices- Which he does by finally sitting with a Cardy who is just trying to be friendly and drinking some Kanar with him- And admitting what the Cardy War had made him become.
It takes O'Brien sneaking onto Maxwell's ship and confronting him about Setlik 3. And a song:
"The Minstrel Boy to the War hath gone, In the ranks of death you will find him. His father's sword he hath girded on, And his wild harp slung behind him."
This song was used to define Miles Edward O'Brien for the rest of his stay on The Enterprise and also on Deep Space Nine.