Northern Ireland lawmakers elected Irish nationalist Michelle O'Neill as first minister on Saturday — a landmark event in a province established more than a century ago to ensure that pro-British unionists would never lose their grip on power.

O'Neill's ascent to the role is the latest sign that her Sinn Fein party's ultimate goal of achieving a united Ireland may be within touching distance.

US President Joe Biden called it an "important step" in a statement and said he looked "forward to seeing the renewed stability of a power-sharing government that strengthens the peace dividend, restores public services, and continues building on the immense progress of the last decades."

What is the importance of this?

The 1998 Good Friday Agreement, also known as the Belfast Agreement, brought with it the end of three decades of sectarian violence over UK rule in Northern Ireland.

Under its terms, intended to maintain a delicate balance between the province's largely Catholic nationalist and mainly Protestant unionist communities, the first minister and deputy first minister essentially share power.

The only real difference in the first-among-equals arrangement is that the first minister greets official visitors to Northern Ireland before the deputy first minister.

The 47-year-old O'Neill had been first minister-designate since May 2022, when Sinn Fein emerged as the largest party in elections for the 90-seat Northern Ireland Assembly.

She will share power with deputy first minister Emma Little-Pengelly from the pro-UK Democratic Unionist Party (DUP). Former DUP leader Edwin Poots was elected as speaker of the chamber.

O'Neill's selection reflects the shifting demographics of the province since the island of Ireland was divided into two states in 1921.

"This is an historic day. It is about the future," O'Neill said on X, the platform formerly known as Twitter, ahead of her swearing-in.

"As a First Minister for All, I am determined to lead positive change for everyone, and to work together with others to progress our society in a spirit of respect, cooperation, and equality."

Why is it happening now?

O'Neill had not been able to take up the role of first minister because of a boycott of the assembly by Sinn Fein's arch-rival, the DUP.

The DUP said it was unhappy about post-Brexit trading rules for Northern Ireland, which shares the only border that the UK has with the European Union.

Under the 1998 peace deal, signed when the UK was a member of the EU, the land border needs to be kept open with no customs checks and infrastructure.

As a result, checks had to be introduced on goods arriving in Northern Ireland from mainland Britain.

The arrangement — keeping only Northern Ireland in the EU single market— upset unionists who feared it risked cutting the province adrift from the rest of the UK. In turn, there were fears that this would make a united Ireland more likely.

The DUP finally agreed to a deal this week after the UK government eased customs checks and other constraints on goods crossing the Irish Sea. That followed the agreement of the so-called Windsor Framework with the EU to make the changes possible.

There were also small legal changes to assure unionists that Northern Ireland's position in the UK is secure, at least for the time being.

A referendum on Irish unity is at the discretion of the British government, which would come under pressure to approve such a vote if it appears likely a majority would seek to join a united Ireland.

When Northern Ireland was formed, the population split was roughly two-thirds Protestant to one-third Catholic. A 2021 census showed Catholics outnumbering Protestants for the first time.

rc/nm (AFP, AP, dpa, Reuters)