A week after the bombing of McGurk's bar in December 1971, a Catholic man and three Protestants - including two infants - died in a no-warning IRA bombing at the Balmoral Furnishing store on Belfast's Shankill Road.
That incident signalled the beginning of the futile scenario of tit-for-tat bombings and shootings by loyalist and republican paramilitaries that were to make the 1970s the nightmare decade of the Troubles. They were years during which no one was safe on the streets of Northern Ireland - especially in Belfast.
In 1971, while the IRA killed an estimated 107 people, loyalist paramilitaries killed 22 - 15 of them at McGurk's bar.
But, by the end of the following year, the ranks of loyalist paramilitary organisations - especially the newly-created Ulster Defence Association (UDA) - had been swollen and the death-toll inflicted by loyalists soared to 121.
By 1974, loyalists were murdering almost as many people as the IRA, reasoning that, if they murdered large numbers of Catholics, then their actions would result in a significant backlash against the IRA and force the organisation to abandon its campaign.
In spite of an IRA ceasefire in 1975, attacks on soldiers and policemen and the slayings of civilians continued with sickening regularity and, as in 1971, the tit-for-tat mentality persisted on both sides of the sectarian divide, resulting in numerous casualties.
In July 1975, the Miami Showband was ambushed by the UVF outside Banbridge in an incident which saw two bombers and three members of the band perish when a bomb exploded prematurely.
A retaliatory attack was expected from the IRA for such a blatant UVF outrage and it came almost exactly a fortnight later when a gun and bomb attack was mounted on the Bayardo Bar on the Shankill Road.
More than 50 people were injured when the old pub structure crumbled, engulfing them in bricks, wooden joist frames, plaster and roof tiles.
Samuel Gunning was chatting to his brother-in-law, William Gracey, who worked in the bar, when the IRA unit arrived at Aberdeen Street in a stolen car and unleashed a fusillade of bullets from an automatic weapon, killing both men.
The gunman's accomplice then walked into the crowded bar and left a bag with a bomb inside it. Customers ran to the toilets in the hope of finding sanctuary, but the bomb exploded, trapping many beneath the rubble - just as the McGurk's bar bomb had done. Hugh Alexander Harris and Joanne McDowell were found dead beneath the rubble and, even though she was pulled alive from the debris, Linda Boyle didn't survive her rescue.
The IRA had explained the attack on the Bayardo as an assault on a pub where individuals associated with the UVF relaxed and planned terrorist assaults against nationalists.
As they were driven away from the attack along Agnes Street, the IRA gang fired indiscriminately at a group of women and children queuing at a taxi rank.
Presumably, they, too, were suspected of planning UVF attacks. The Provisionals didn't admit responsibility for either attack, but in a statement three months previously its leadership had ominously warned that 'retaliatory and defensive actions' could be sanctioned after a loyalist attack was perpetrated.
Two days after the Bayardo massacre, Samuel Llewellyn - a Protestant who worked for Belfast City Council - was abducted and murdered by republicans on the Falls Road to where he had been despatched to ferry materials to board up buildings damaged in a loyalist bombing. He too, seemingly fell to the 'retaliatory' strategy prevailing within the IRA.
The IRA responded to the Falls bombing with an attack on the Protestant-owned Travellers Rest Inn near Twinbrook which killed Cecil Anderson and in Armagh, another Protestant, Norman Kerr, was shot dead.
The two-day period vividly illustrated that, when stirred to display sectarian hatred, the IRA was just as despicable as the loyalists who bombed McGurk's and attacked the Miami Showband.
Many years later, Gerry Adams told me that Brendan 'Bic' McFarlane, sentenced to life imprisonment for his role in the Bayardo Bar massacre, "hadn't a single, sectarian bone in his body".
Perhaps he hadn't, but those who directed him undoubtedly did. The Bayardo Somme Association describes the incident as "a forgotten atrocity". McFarlane, a former student priest, was elevated to Officer Commanding IRA prisoners at the Maze and was influential in the negotiations that led to the 1994 IRA ceasefire.
In April 1975, the chilling reality of sectarian revenge bombings was starkly illustrated on Grand National Day, when the UVF exploded a bomb in the doorway of McLaughlin's Bar on the Antrim Road, killing two young Catholics.
Before the National had finished, the IRA was putting in place a plan to bomb the Mountainview Tavern on the Shankill Road, killing five Protestants.
Not sectarian bones, rather clear sectarian intentions drove the IRA in the era after the McGurk's bar atrocity.