Tensions are high in Northern Ireland as President Biden heads to the region. Here's why.

President Biden will travel to Northern Ireland Tuesday to mark what the White House calls the "tremendous progress" in the 25 years since the signing of the Good Friday Agreement, which ended decades of violence in the region. He will then head to the Republic of Ireland, where he will meet with officials and explore his Irish ancestry.

Mr. Biden's visit to Belfast, the capital of Northern Ireland, will "underscore the readiness of the United States to support Northern Ireland's vast economic potential to the benefit of all communities," the White House said in a statement last week.

But it comes amid increasing tensions in the region as old sources of discord resurface.

• A small town on Ireland's coast is eagerly preparing for a Biden visit

What is the Good Friday Agreement?

Northern Ireland is part of the United Kingdom. For 30 years, from the 1960s to the 1990s, those who supported reunifying Northern Ireland with the Republic of Ireland – predominantly Catholics referred to as "republicans" – fought a violent sectarian campaign against those who wanted to remain part of the U.K., made up mostly of Protestants known as "unionists." Dubbed "The Troubles," the conflict resulted in the deaths of over 3,500 people. 

The Good Friday Agreement was signed on April 10, 1998. It got both sides of the conflict to lay down their arms and set up a local government for Northern Ireland in which power was shared between republicans and unionists. It says that Northern Ireland is part of the United Kingdom, and that this can only change through a referendum. It also says people in Northern Ireland can have both British and Irish citizenships.

As part of the agreement, armed groups agreed to get rid of their weapons, and people who had participated in the violence were conditionally released from prison. The U.K. government also agreed to aim to scale back their military presence in Northern Ireland.

Increasing tensions

But ahead of the president's arrival on Tuesday, tensions are high, as post-Brexit trade issues have created new political pressures that prompted British unionist politicians to withdraw from the power-sharing government last year.

Despite the signing of a new trade deal between the U.K. and the EU last month, Northern Irish unionists are refusing to return to the government. They say the deal leaves some EU laws in place that would pull Northern Ireland closer to the Republic of Ireland — an EU member — and further from the U.K., which is no longer a member of the EU.

Last month, U.K. authorities raised Northern Ireland's terror threat level from "substantial" to "severe" due to threats from dissident republicans.

Young protesters pelted a police car with molotov cocktails as predominantly Catholic republicans mrched through the city of Londonderry on Monday, and a Protestant parade took place in Belfast, CBS News' Charlie D'Agata reports. The parades happen every Easter, but with tensions rising, they're taking on added significance, D'Agata says.

On Sunday, the Belfast Telegraph reported that police uncovered a republican dissident bomb plot to coincide with Mr. Biden's visit, though experts said the President himself would probably not be targeted in any attack.

"An attack of some sort is deemed to be potentially imminent, but that's not a threat against the U.S. President because for years, you know, for better or for worse, they [republican dissidents] have had significant support from the United States," Jim Gamble, former head of counter-terrorism in Northern Ireland, told CBS News.

After his visit to Northern Ireland, Mr. Biden will travel to Ireland for three days to visit County Louth, where his great-grandfather was born, and County Mayo. He will meet with the Irish president, Michael D. Higgins, the Irish Prime Minister, Leo Varadkar, and address a joint session of the Irish parliament.

In:
• Joe Biden
• Northern Ireland
• Ireland

Haley Ott

Haley Ott is an international reporter for CBS News based in London.

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