@Patrick
It's tribalism mate. The Irish fans are very passionate and it shows at every international tournament (well, the few we qualify for !).
From a club perspective, the English League was/is the biggest show in town and a lot of Irish started supporting Liverpool because so many Irish moved over there and that created a connection.
I think the united thing came from the fact that there needed to be a rival and they were the obvious choice, coupled with the fact that a few top Irish players played for them at one point?
Anyway, as far as the Premier League goes, this was never meant to happen. They're basically confused. They were meant to do battle with each other and that's dead now, so they are bitter about it and it results in the media constantly talking about "real" football being dead, or the fact that City aren't a "real" club.
In a nut shell, we have taken their "reality" away from them.
All that said, this one isn't too bad:
https://www.irishexaminer.com/sport/soc ... 79748.html