Leaders call for calm after a week of unrest in Northern Ireland

Details: On Wednesday night, people threw bricks and gas bombs at a "peace wall" that separates Protestant and Catholic neighborhoods in Belfast, and set a hijacked bus on fire. The nation's police service said 55 officers have been injured in the nights of violence this week, per AP.

What they're saying: "We are gravely concerned by the scenes we have all witnessed on our streets," said the Northern Ireland Executive Office in a statement.

• "All communities in Northern Ireland must work together to resolve the tensions that we are currently facing," said Britain's Northern Ireland Minister Brandon Lewis in a statement, per Reuters.

Between the lines: Many find the recent violence and tension in Northern Ireland concerning because they bring to mind 'The Troubles' in Northern Ireland — the nearly three decades of violence between Protestants and Catholics that killed more than 3,000 people and injured 50,000.

• The Good Friday Agreement of 1998 ended the violence and set up a power-sharing government, and its lack of a hard border — when both the U.K. and Ireland were part of the EU — allowed people on both sides of the divide in Northern Ireland to identify with either side they wished.

Brexit has upset this delicate balance, since it created a de facto border in the Irish Sea, as goods now entering Northern Ireland from Britain are subject to EU checks and tariffs and left some citizens feeling isolated from Britain, per Reuters.