The Ardoyne district of Belfast has once again lived up to its reputation as one of Northern Ireland's most violent areas, with more than 100 police officers injured in disturbances on Thursday night and yesterday morning.
Hours of rioting saw pitched battles between nationalist youths and RUC riot squads, with one officer felled by a pickaxe and others coping with petrol bombs and blazing hijacked vehicles.
It is almost certain that the IRA either planned or took over the incident, given that the organisation and Sinn Fein are the strongest influences in the district.
With the question of future policing arrangements featuring prominently in the political talks taking place in England, the violent exchanges represent a potent, if contrived, republican method of illustrating in the most graphic way that the RUC is unacceptable to local Catholics.
On a longer timescale, however, the fighting represents simply one more battle in a long-simmering conflict between Protestants and Catholics that has gone on for decades on this contested Troubles fault line.
Republican Ardoyne sits uncomfortably close to the loyalist Woodvale and Crumlin Road areas. Much of the Catholic district is surrounded by peacelines, but part of it is open to allow access. In the course of recent decades the balance of power has shifted imperceptibly but decisively as Protestant numbers have dwindled and the Catholic population has increased.
Loyalist paramilitary organisations on the margins of Ardoyne now have a sense that they must combat what they see as Catholic encroachment into what was previously identified as Protestant territory.
Last month this resulted in serious clashes, in which many injuries were caused, after a sectarian dispute flared. On that occasion a relatively minor incident escalated into serious rioting involving police, republicans and loyalists.
On Thursday night the latest bout of rioting broke out as Orangemen who had just taken part in the main annual 12 July demonstrations made their way home. Mindful of last month's violence, a strong police presence was on hand.
According to the local Sinn Fein assembly member, Gerry Kelly, a peaceful protest was being staged against the march when people were "provoked by the RUC".
He said: "There were stewards on the ground, they were keeping things calm and the water cannon and batons were turned on them. Once you attack the stewards who are trying to calm the situation, how do those people then keep control?"
The RUC Chief Constable, Sir Ronnie Flanagan, said the trouble had been planned, indicating that he believed the IRA was the driving force behind it. He added: "People do not spontaneously have to hand acid bombs, blast bombs, and angle grinders to cut down lampposts to block roads. This was orchestrated. I have little doubt about that."
In all about 250 petrol bombs and two blast bombs were thrown during seven hours of violence. Police replied with almost 50 plastic bullets, making several baton charges. At one stage a petrol station was set alight by rioters.
The Chief Constable declared: "If police had not acted in the way they did, what we would have faced was the most serious intercommunal violence. Had we not been there lives would have been severely and imminently put at risk."
Although this year's marching season has actually produced less trouble than most recent years, disturbances have flared in a number of areas, chiefly in Belfast and Portadown, Co Armagh. There has also been the familiar rash of cases of petrol bombings and other attacks on homes.
In one case on Thursday serious disturbances broke out between rival loyalist factions during a major Orange Order march, with seven people injured in Shaftesbury Square, close to Belfast city centre.
In an unexpected re-enactment of history, police and eye-witnesses said that ceremonial swords, pikes and banner poles carried by marchers were wielded as weapons during hand-to-hand fighting.
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