The McCarthy-Dundon and Keane-Collopy criminal gangs have been vying for control of the lucrative drugs trade in the mid-west region.
The feud began with the murder in 2000 of killer Eddie Ryan, who was an associate of brothers Christy and Kieran Keane.
Journalist Paul Williams writes in his book, Crime Wars, that Ryan was an enforcer for the two Keanes, who had established a criminal empire in the mid-west region from the early 1990s.
Ryan, who had a criminal record for armed robbery and violence, fell out with the Keanes and on November 12, 2000 he was shot in the Moose Bar by Kieran Keane.
Ryan's son Kieran was in the toilet when his father was shot.
If he had been with him, he would almost certainly have been killed as well.
Days before the shooting, Eddie Ryan had attempted to murder convicted drugs dealer Christy Keane in a bid to establish himself as a major criminal player in the city's murky underworld.
The murder of Ryan sparked a major upsurge in violence.
In the intervening eight years, there have been countless shootings, arson attacks, threats issued and violence inflicted by both sides.
Gardai have seized weapons on a regular basis, including Desert Eagle handguns, AK-47 assault rifles, rocket launchers and grenades.
Criminal cases have been dropped amid fears of witness intimidation and gang members have been sent to New York, Florida and eastern Europe on gun-training courses.
Williams writes: "When it came to producing hard, violent men, Limerick had always stood out from the rest of the country. But no one had ever seen the likes of the Dundons and their entourage of hate-filled thugs."
During one incident, gardai from Roxboro Road Garda Station, who were investigating the theft of circus horses, called to the Dundon's home at Hyde Road to arrest Dessie Dundon, then aged 20.
Wayne Dundon launched a savage attack on Detective Garda Pat Cox and his partner Detective Garda Brian Lynch in a bid to free his brother.
Det Gda Cox suffered serious injuries to his arm and shoulder as he tried to protect himself and he never worked in active service again.
In January 2003, Kieran Keane was duped by the Ryan gang into travelling to an isolated spot at Drombana outside Limerick with his nephew Owen Treacy for a meeting.
Keane was overpowered and shot in the head. The gun then jammed and the gang stabbed Treacy 17 times.
Remarkably, he survived and gave evidence against five members of the Ryan-McCarthy-Dundon gang.
They are all serving life imprisonment.
John Ryan (47), a brother of Eddie Ryan, was shot dead as he worked on the patio of his home at Canon Green Park in Thomondgate in July, 2003.
He had moved there after being the subject of some 30 gun attacks at his previous home in St Mary's Park in the Island area.
Other feud-related deaths included the killing of Frankie Ryan (21) in September, 2006.
He was a member of the Ryan-McCarthy-Dundon gang and was shot dead as he sat in his car in Limerick's Moyross.
From about this point the McCarthy-Dundon faction assumed control of the gang from the Ryans.
In April, 2007, Noel Campion (35), a former associate of the Keanes, was ambushed and shot dead near Limerick city centre as he sat on the back of a motorcycle.
He was blamed for carrying out the murder of Frankie Ryan.
The feud boiled over again in April this year with the murders of Mark Moloney (40) and James Cronin (20).
Cronin was shot dead later the same evening as the McCarthy-Dundon gang killed Moloney. Cronin was not a serious criminal but had been recruited to drive the car used in the Moloney killing. The gang apparently began to suspect Cronin might give evidence to gardai and executed him.