The violence intensified in the early 1970s , with rival paramilitary groups being formed on both sides . Bombing , assassination and street violence formed a backdrop to life throughout The Troubles . The PIRA detonated twenty-two bombs , all in a confined area in the city centre in 1972 , on what is known as " Bloody Friday " , killing nine people . Loyalist paramilitaries , the Ulster Volunteer Force ( UVF ) and Ulster Defence Association ( UDA ) retaliated against the PIRA campaign by killing Catholics at random from around August 1972 onward . A particularly notorious group , based on the Shankill Road in the mid 1970s became known as the Shankill Butchers
Bloody Friday
Bloody Friday (1972)
History of Belfast