On the night of 15 August 1969, a Protestant mob burst into the Catholic part of west Belfast and burned down houses in and around Bombay Street, forcing the Catholic population to flee. The pogrom had a traumatic impact on Catholics in Northern Ireland, delegitimising the authorities for tolerating or assisting the mob, and playing a key role in the creation of the Provisional IRA.

On Wednesday night this week, a Protestant mob from the Shankill Road used cars to smash their way through the massive steel gates in the so-called peace wall dividing Protestants from Catholics in west Belfast. “The attack was very dangerous,” says Brian Feeney, a historian and columnist on The Irish News, taking place as it did close to a rebuilt Bombay Street and reawakening old terrors. “If the mob had broken through (the steel gates), they would probably have been met with gunfire.”

Reports on violence in Northern Ireland over the last week — the worst for decades according to the police — fail to understand that rioting in the province is of two types that look the same but have very different impacts. One is skirmishing with the police by setting fire to vehicles and hurling stones, petrol bottles and fireworks. Dangerous though this is, it has been practised by both communities at different times to advertise their grievances, on the correct presumption that events in Northern Ireland will be ignored by people in mainland Britain and the wider world unless there are dramatic scenes of violence to grab their attention.

But there is another much more dangerous type of rioting in which one community is pitted against another and which awakens memories of past sectarian blood-letting. This is what gives that attack launched from the Protestant Shankill Road towards the Catholic Springfield Road in west Belfast this week such deadly potential. “It is so depressing,” said a friend in Belfast with long experience of the conflict. “This is the sort of thing I thought we had left behind us.” Sectarian hostility between the Catholics and Protestants never died away, but for 23 years the Good Friday Agreement (GFA) has kept a rough-and-ready balance of power between the two communities that is now close to breaking down. My friend in Belfast, who lamented the return to old animosities, puts much of the blame on the first minister and Democratic Unionist Party (DUP) leader Arlene Foster. “She is incredibly incompetent,” he says, and she certainly has a record for inept opportunism that weakens her own community and exacerbates sectarian friction.

Yet there is more to the escalating conflict than the failings of Foster and the DUP. Unionists determined to keep Northern Ireland part of the UK are facing a more general crisis. The origins of this go back to the ending of the Protestant-dominated statelet after what was politely called “The Troubles” but was really a vicious low-level war lasting 30 years. Demographically the Protestants are slowly losing out. They constituted two-thirds of the population when the Northern Ireland state was established a century ago, but are now probably less than half of it — something that will become clearer with the publication of the latest census figures next year. Sinn Fein may become the largest party in the assembly election in May 2022, and thus able to appoint a first minister.

Such long-term trends might have been absorbed peacefully, but they have been envenomed by the UK voting to leave the EU in 2016, though the province voted solidly Remain. The decision automatically reopened “the Irish question”, which had poisoned British politics for over 200 years, and which the GFA had temporarily put to rest. The partition of Ireland once again became a live political issue, to the delight of Sinn Fein. The 300-mile-long border between Northern Ireland and the Republic is now the international frontier between the UK and EU. But, since the abolition of a hard border is an essential provision of the GFA, this border runs down the Irish Sea.The DUP briefly held high political cards between 2017 and 2019 because it kept a minority Conservative government in power at Westminster. But it overplayed its hand catastrophically, put its trust in Boris Johnson’s hand-on-heart promises about rejecting any Irish Sea border, and ended up by accepting the Irish protocol, which was the worst possible option from the unionist point of view.

Graffiti saying “Kill the protocol” began to appear on walls in Protestant districts earlier this year as new regulations on trade between mainland Britain and Northern Ireland were applied. These regulations may not be particularly significant in commercial terms, but they looked like one more very visible wedge splitting the union.

More worrying for the DUP, an opinion poll in February showed it to be well behind Sinn Fein and losing support to the hardline Traditional Unionist Voice. Floundering about and looking desperately for a policy, the DUP turned against the protocol, and is seeking vainly to replace it. But at the same time their leaders — since they head the Northern Ireland Executive — are meant to implement it.

Foster and the DUP fell back on a “dead cat” strategy — making a dramatic gesture to divert attention from their missteps. The result is that Foster is demanding that the head of the police service of Northern Ireland, Simon Byrne, should quit because of the failure to prosecute members of Sinn Fein who allegedly broke COVID-19 restrictions by attending the funeral of IRA leader Bobby Storey last June.

In fact, the decision not to prosecute was taken by the director of the Public Prosecution Service because there was no chance of a successful prosecution. The COVID-19 regulations “had been amended on nine separate occasions” in a short period of time, and nobody quite knew what they were. After protests, this decision is now being reviewed.