IRA and PIRA, who are they?

I.R.A and P.I.R.A.: I.R.A. was an Irish republican revolutionary military organization. It was descended from the Irish Volunteers, an organization established on 25 November 1913 that staged the Easter Rising in April 1916. In 1919, the Irish Republic that had been proclaimed during the Easter Rising was formally established by an elected assembly (Dáil Éireann), and the Irish Volunteers were recognized by Dáil Éireann as its legitimate army. Thereafter, the IRA waged a guerrilla campaign against British rule in Ireland in the 1919–21 Irish War of Independence. Following the signing in 1921 of the Anglo-Irish Treaty, which ended the War of Independence, a split occurred within the IRA. Members who supported the treaty formed the nucleus of the Irish National Army founded by IRA leader Michael Collins. However, much of the IRA was opposed to the treaty. The anti-treaty IRA fought a civil war with their former comrades in 1922–23, with the intention of creating a fully independent all-Ireland republic. In the 1960’s, the IRA became violent and began to protest against the separation of Northern Ireland, which was called the Provisional IRA campaign, where there had been conflicts between unionists and nationalists for a long time. Unionists are overwhelmingly Protestant, descendants of mainly Scottish, English, Welsh and Huguenot settlers as well as Old Gaelic Irishmen who had converted to one of the Protestant denominations. Nationalists are predominantly Catholic and descend from the population predating the settlement in Ireland. Provisional IRA actively caused armed terrorism in Northern Ireland from 1969 until 2005 when the IRA Army Council announced an end to its armed campaign.

For more information – http://www.cfr.org/separatist-terrorism/provisional-irish-republican-army-ira-aka-pira-provos-glaigh-na-hireann-uk-separatists/p9240