ALTHOUGH this weekend's clashes are centred on Twelfth of July demonstrations – which see Northern Ireland's Protestant community celebrate the victory of King William of Orange over Catholic King James II at the Battle of Boyne in 1690 – this year's unrest has the added incendiary element of being fuelled by the recent flag protests.

Violent demonstrations have been going on sporadically since early December last year when Belfast City Council controversially voted to limit the number of days that the Union Jack flies over the City Hall.

Since 1906, the flag had been flown every day of the year.

The move was proposed by the council's Irish nationalists, who wanted to take it down permanently but was opposed by unionist councillors. The council used to be dominated by unionists: the Democrat Unionist Party (DUP) and Ulster Unionist Party but, in May 2011, Irish nationalists – Sinn Fein and the Social Democratic and Labour Party – won more seats than unionists for the first time.

The middle-ground Alliance Party, which holds the balance of power in the council, put forward the compromise that the flag would fly on just 18 designated days.

On the night of the vote on December 3, protesters stormed City Hall, signalling the start of a prolonged bout of extreme loyalist violence.

Loyalist protesters set up daily road blocks while carrying union flags and banners and targeted the Alliance Party offices and the homes of party members.

Belfast City councillors were sent death threats and there was a reported rise in sectarian attacks on Catholic communities.

The demonstrations inevitably led to clashes with police.

Officers were attacked with petrol bombs, paint bombs, fireworks, smoke canisters and stones, while rioters damaged vehicles with sledge hammers. Police, heavily armoured in riot gear and batons, used water cannons and shot plastic bullets at the rioters.

Several officers were injured but Police Service Northern Ireland (PSNI) chief constable Matt Baggott vowed to do "everything possible" to maintain order and deal firmly with those who broke the law.

As the unrest spread, a gang of men attacked a police car guarding Alliance Party MP Naomi Long's office in east Belfast. They smashed the window and threw in a petrol bomb while a policewoman was still inside, but she escaped unharmed.

In Armagh, protesters attacked a pub owned by the husband of a Sinn Fein councillor. The windows were smashed and fireworks thrown inside. Several other protests erupted throughout December and carried on after the festive period and into the new year.

In early January, gun shots were fired at police during clashes in east Belfast. In early February, the violence subsided marginally but tensions remained high and protests continued to happen sporadically.

On April 20, Belfast City Council rejected a DUP proposal to fly the union flag every day on the centotaph in the grounds of City Hall.

Unionist councillors voted in favour of the proposal but Irish nationalists and Alliance councillors voted against it. The Royal British Legion was also against the proposal, saying it did not want the cenotaph to become politicised.

The cost of policing the protests, up to March this year, has been estimated at £20 million.

The widespread disruption, turning the streets of Belfast into a battle ground, has also had a severe impact on tourism and business development in Northern Ireland.

Flag protests are estimated to have cost businesses more than £10m so far.