The only reason for bringing up the Irish situation is that it illustrates a situation where continued military intervention was only really stopped when the status quo of violence was trumped by the majority marginalising the extremists.
Of course ISIS is a different problem in many ways but it is backed by an ideology that allows the extremism to breed beyond national borders and loyalties. Military intervention over the past 25 years has not stamped out Islamic extremists. It has not marginalised the thinking of these lunatics. The people to change Islam are Moslems.
Extreme behaviour by "Christian" nations stopped when the West became more secular, less dogmatic and more tolerant. It has taken hundreds of years but the pace of change has increased as less and less people have bought into the prejudices that religious belief allows to be propagated.
islam is along way behind but I only see real change coming as the ideology gets marginalised as more and more people are secularised and educated. Making that happen in the Moslem world is the challenge.