The difficulty is compounded by three things: first, the west is undefeatable in military terms, and acts of terrorism serve to underpin the west's resolve, not to undermine it. Secondly, however, the hydra-like nature of ISIS/AQ means that they too are undefeatable in military terms. We learned in Northern Ireland that asymmetric wars are unwinnable. In military terms western backed powers will before too long take back the territory under IS control, but that won't end the conflict any more than did taking Afghanistan from the taleban.
Which brings me to the third point, namely that some form of negotiated settlement is the only way this conflict can end. I take your point that it is difficult to imagine the suicide bombers sitting round the negotiating table, but some time (even if it is decades away) the higher echelons in IS/AQ will come to the table, because however long it takes it will eventually dawn on them that they can't win.
Not sure I agree with your conclusion about the outcome of the Troubles. The British Government only had one stated aim in that conflict, a conflict which came to their door it should be said, namely that Northern Ireland remained part of the UK as long as its people continued to will it as such. That is where we find ourselves today, so it's difficult to see how anyone could say that they British lost that 'unwinnable' conflict.
That point, however, is more than a little trite. Putting the organised crime element to one side, even the most radical of Irish Republicans aspired to a representative democracy in a united Ireland where (theoretically at least) Unionists were to be welcomed into that society. Catholics in Ireland have a much better record of tolerance to Protestants than the other way round (although that is straying slightly off the topic, it underlines my point). Moreover, even at the height of the Troubles, in the early 70's, there was dialogue at the highest levels between the IRA and the British Government. That is because they were two highly disparate and divided bodies, but they shared relatively similar perspectives about how to order society.
With IS, you may as well be talking about people who think the moon is made of cheese. There is no common ground between the two groupings. They want to obliterate western society , as they see it as utterly immoral and dissolute. Equally, as a society, we will not accept anything that imposes itself on our way of life, most certainly to that extent. There isn't and can not be any common ground. Not sure how that can ever be a basis for dialogue.
As I said, I don't expect troops on the ground to act as any panacea, or any long term solution, but until one presents itself there will be occasions to cut off the head or one of the heads off the hydra in the knowledge that it will, in all probability, grow back again.
I think that time has come.
