Yes, most fascinating history, which somehow refuses to stay that, history... Someone (Iain Banks, someone here?) said that the main obstacle to peace in Northern Ireland is "whataboutism": whenever the peace is within reach, someone would stand up and say "Yes, but what about <this or that ancient injustice>!?", and we are back to square one.

Now, here is a heretical idea: perhaps solution lies in better integrated "Europe of regions", where nation states, while still existing, are not the obstacle to different, sometimes more natural organization. Irish/British Ulster is far from being the only example: Spanish/Frensh Basque region, French/German Alsace/Lotharingia, Italian/Slovenian/Croatian Istria, Italian/Austrian Tirol... Europe has very turbulent history, and existing borders are best left alone, but there is hardly a pair of neighbouring countries that do not share some such region spanning national borders.