From Wikipedia

The Troubles

Episode Five

The years 1970–1972 saw an explosion of political violence in Northern Ireland, peaking in 1972, when nearly 500 people, just over half of them civilians, lost their lives. 1972 was the year which saw the greatest loss of life throughout the entire conflict. There are several reasons why violence escalated in these years.

Unionists claim the main reason was the formation of the Provisional Irish Republican Army (Provisional IRA), a group formed when the IRA split into the Provisional and Official factions. While the older IRA had embraced non-violent civil agitation, the new Provisional IRA was determined to wage "armed struggle" against British rule in Northern Ireland. The new IRA was willing to take on the role of "defenders of the Catholic community", rather than seeking working-class unity across both communities which had become the aim of the "Officials".