Explainer: What's causing the unrest in Northern Ireland?

Hundreds of youths in the British province’s capital Belfast set a hijacked bus ablaze and pelted stones at police on Wednesday, causing growing concerns over the long-term prospect of peace in Northern Ireland.

With more violence expected, what are the main issues fuelling the unrest and will peace ultimately endure?

Who is behind the violence?

The unrest is mainly emanating from the unionists -- who believe that Northern Ireland should remain part of the United Kingdom -- with police warning that paramilitary groups within the community could be stoking and coordinating violence.

Nationalists, who believe the province should be part of the Irish Republic, responded to the violence on Wednesday and the two groups attacked each other with petrol bombs and missiles.

Where are the focal points?

Violence flared last week in the city of Londonderry, before spreading to the capital Belfast and outlying areas over Easter weekend and into Monday.

The latest unrest was focussed on the "peace line" -- a series of walls separating nationalist and unionist neighbourhoods.

Why are unionists angry?

Much of the unrest stems from unionist anger at a new post-Brexit "protocol", which they believe drives a wedge between the province and the rest of Britain, drawing it closer to Dublin´s orbit.

"There is no doubt that Brexit and the advent of the protocol have significantly damaged the balance of power," Duncan Morrow, a political science professor at Ulster University told AFP.

"This has been brewing for months."

Why was the protocol introduced?

Unionists and nationalists waged a decades-long conflict, referred to as "The Troubles", over the future of the province until a landmark peace deal in 1998.

This dissolved border checks on the Irish border as both sides of the divide were in the European Union and part of the single market.

Britain´s 2016 referendum decision to leave the bloc threatened to upset that arrangement, raising the spectre of border checks that went against the peace deal.

To keep the border open while maintaining the integrity of the now separate markets, Britain and the EU agreed on the "protocol", which effectively keeps Northern Ireland in the EU´s customs union and single market.

While keeping the Irish border open, it now means checks are required on goods arriving in Northern Ireland from elsewhere in Britain, which unionists say signals a loosening of ties with the UK.

What are the everyday effects of the protocol?

Since it was implemented in January, the protocol has disrupted trade and triggered some food shortages in the province.

The new checks have caused widespread confusion among businesses, with some UK suppliers refusing to ship goods across the Irish Sea, leading to some bare shelves in Northern Irish supermarkets and customers there unable to order items online.

Will the protocol survive?

The EU stresses that the protocol is a done deal, and has already launched legal proceedings against Britain over allegations that it broke its rules by unilaterally announcing a six-month delay of custom controls on goods arriving in Northern Ireland from mainland UK.

But the Democratic Unionist Party (DUP) has sought a judicial review, wanting courts to declare the protocol incompatible with the 1800 Act of Union that merged the kingdoms of Britain and Ireland, and with the 1998 Good Friday Belfast Agreement.

In the longer term, the protocol provides for a "consent" mechanism, which from 2025 gives the Northern Ireland Assembly the power, by majority vote, to discontinue its application.

Is Brexit the only issue?

Brexit is only one of many grievances among unionists.

Unionists lost their historic majority at the regional assembly at Stormont in 2017 and there is evidence of a demographic shift towards nationalists, feeding a sense of them being a besieged minority.

Riots also flared after authorities decided not to prosecute leaders of nationalist party Sinn Fein for attending the funeral last year of a former paramilitary leader in apparent breach of the Covid restrictions that have kept residents cooped up for the best part of a year.

Is the peace process at risk?

Around 3,500 people were killed in The Troubles, and experts fear that Brexit could be the straw that breaks the back of hard-won peace, given the underlying resentment and complexities.

"It remains very hard to see where it goes except for mounting frustration and anger," Morrow warned.