I've been diving back into Crusader Kings II recently, and recently I've been trying to see how far I can get with the Ua Brian family (currently, I've managed to unify Ireland, and conquer Wales, Brittany, and Scotland). Obviously, that's a computer game (and I may have given myself some...start up money, and I got supremely lucky in that both England and Scotland imploded into civil wars while I was consolidating power), but it has got me wondering: how far could Medieval Ireland have gone?
Would one of the Petty Kings been able to unify the island before the Normans invaded in 1167? If Kingdom had managed to unify, would they have been able to "reverse" history and mount invasions of Scotland/England/Wales? Assuming everything "breaks" for Ireland, how far could they have gone?