LONDON — A bus hijacked, pelted with stones, then set on fire. Masked youths rioting, hurling missiles and homemade bombs. A press photographer attacked on the streets.
For almost a week, scenes of violence familiar from Northern Ireland’s brutal past have returned in a stark warning of the fragility of a peace process, crafted more than two decades ago, that is under growing political and sectarian strain.
Amid a contested fallout from Brexit, politicians have pointed to different causes for an explosion of anger from parts of the Protestant, so-called Unionist or Loyalist, community that is determined to keep its link to the rest of the United Kingdom.
But analysts agree that six consecutive nights of violence, during which 55 police officers have been injured and 10 arrests made, mark a worrisome trend.
Britain completed the final stages of Brexit on Jan. 1. That ended a system under which companies in Northern Ireland shared the same trade rules as those of Ireland, which remains part of the European Union.
During the interminable Brexit negotiations, much energy was devoted to preventing the need for checks on goods at Northern Ireland’s highly sensitive land border with Ireland.
Under an agreement in a protocol struck by Mr. Johnson, Northern Ireland was given a special economic status that leaves it straddling the United Kingdom and the European Union trade systems.
suspend the protocol by triggering an emergency mechanism in a dispute over vaccine supplies. Though the British government had also threatened to break the treaty over a separate issue — and the European Union reversed its decision within hours — that united Unionists in anger.