Jason's a godsend on this subject as he understands it so well.
I think it correct to say the modern age of The Troubles that saw the ascendancy of PIRA is what most people think of. Both sides appropriate heroes and symbols from ages ago to reinforce the sense that their side has a glorious history and shall surely prevail. These things serve to extend the conflict, to embed people deeper into it and thus cultivate patriotic furvor.
It's worth noting that when Britain decided to first send troops to Northern Ireland in 1969 following the Battle of the Bogside, both sides welcomed them with open arms. The Royal Ulster Constabulary (RUC) were distrusted by people on both sides for its partisan factions, disciplinary problems, and the gross mishandling of some unfortunate cases such as the 1968 civil rights marches where unarmed protesters were attacked. The RUC was also completely unprepared for armed violent conflict as it proved in the Bogside. The army seemed the answer.
It was thought the army would restore peace and order. That idea was promptly defenestrated when it became obvious to the republican factions that the army were not going to leave after a few months as had been promised by the British government. This is when Provisional IRA split from the IRA (not the so-called Real IRA) and things went downhill. In 1971, Westminster introduced internment. Internment was the ability of the government to hold whomever, whenever, and for however long the government wanted. In one night over 300 people were picked-up by the black mariahs and disappeared. It was noted that great majority of those interned were republican sympathizers, real or alleged. The protests against the government became huge and some people, again republicans, were killed.
And in light of that came the biggest fuse yet. Peaceful, unarmed republican demonstrators protesting internment marching on January 30, 1972 were fired upon by British troops who believed they were under attack. Inquiries have since suggested that there may have been a lone person who did fire a gun, but it must be noted that PIRA told people not to have weapons and anyone caught with one in the area would face some unsavory consequences. Sinn Fein wanted their peace marches to be peace marches. In any event, a massacre occured and 14 people were killed including children and bystanders. That's known as Bloody Sunday. An independent tribunal, now known as the Widgery Tribunal, found the soldiers largely blameless for shooting at unarmed protesters and yet another nail in the coffin of peace was countersunk as the Widgery Tribunal findings were held in disbelief by a very large population of people on both sides of the conflict who saw it for it was, a whitewash.
If people had been uncommitted up to that point, few were after it. The republicans saw themselves as victims, under the thumb of British forces who appeared to be taking sides in the conflict, and so protested to their homerule government. No use. Home rule was suspended later on in 1972 and northern Ireland came under the direct rule of the British parliament. That act angered many more republicans who now felt as if their political power had been taken away despite the fact that they were British, carried British passports, and paid their taxes to London.
Things just went from bad to worse after that.