The final point to remember with terrorism is one of motivation. Terror attacks only work to achieve the terrorists' aims if they are very carefully targetted and choreographed along with a political campaign, to make them look like attacks against a mutually-disliked foe. This is why the IRA in Eire and Northern Ireland are largely silent these days; they changed from being seen as freedom fighters to being thought of as a general blight upon the entire society. Islamic terrorists are already being cast as such a blight, and never really get the chance to put over their side of the argument.
The IRA in the Irish Republic largely achieve it's aims, independence from Britain and they are not exactly gone. They supported the IRA in N-Ireland operationally and logistically throughout the troubles. As for the IRA in N-Ireland they weren't exactly angels but then the UVF wasn't exactly a legion of boy scouts either (anybody remember the Shankill Butchers?). I'm not in favor of either organization but the IRA does have one good point: the Irish situation in its entirety is a witches broth cooked up by the British and they deserve no pity when they complain about it's foul taste. Whether intentionally or not, by stamping the IRA 'terrorists', you simplify the situation in Ireland and make it sound as if the IRA 'terrorists' unbalanced a previously peaceful British province where everybody lived in harmony and contentment. Britain built a society in Ireland where Catholics were second class people and it is not surprising that when the Catholic challenges of that social order during the 20th century caused the Protestant elite to feel threatened, the ongoing and centuries long project of brutal religious and ethnic reengineering of Ireland blew up in the Britain's face (yet again). That is the real root cause of the Irish troubles. Organizations like the IRA, UVF and for that matter ISIS, Hamas and the likes are just a symptom of some deeper problem.