A century later, Northern Ireland is set for another historical upheaval

The Brexit deal will almost certainly benefit the country but the Union will be exposed once again by age-old issues

In this file photo taken on October 1, 2019 a vehicle passes an anti-Brexit pro-Irish unity billboard seen from the Dublin road in Newry, Northern Ireland. AFP

Wednesday marked the 100th anniversary of the enactment of a British law that allowed the partition of Ireland, then under UK control, into two spheres – Northern Ireland and Southern Ireland, with the latter eventually becoming the Irish Free State.

The 1920 Act, as it is commonly known, was introduced to provide for the "better government" of Ireland. It brought no such thing. It was eventually repealed in 1998 with the Good Friday Agreement, which put an end to the decades-long conflict in Northern Ireland between the Unionists and Nationalists, and made way for a devolved system of government there.

Next year's planned centennial commemorations for Northern Ireland, which got its own parliament after the act, are likely to spur further division. In the context of Brexit, the distancing of Northern Ireland from the UK is newly set in train. An existential question of how the Protestant/Loyalist and the Catholic/Nationalist communities share the space moves into a new phase.

On Thursday, the EU-UK trade deal confirmed Northern Ireland as a place apart. Yet, Thursday's outcome cannot be a settled set-up for its residents.

There has been plenty of attention given to the Scottish resentment of the pact and the threat to the integrity of the UK. However, it is Northern Ireland that has already entered an unprecedented hybrid status.

A careful read of the UK customs advice on future commerce with the EU reveals a new code for all transactions starting with the letters "GB" – or Great Britain – as opposed to "UK". As a whole, the UK encompasses Northern Ireland.

Letters matter. Northern Ireland trade remains in the EU’s Customs Union while also included in the UK economy.

A century on from the last big shift, Belfast is ripe for another historical upheaval. How the 100 years of the Northern Ireland campaign goes down in 2021 is crucial to the future, not just the past.

So far the signs are not good.

The government there is currently planning celebrations to mark the centenary of its establishment. The institutional dynamic of the celebrations is that there is something for everyone to be happy about. But Northern Ireland does anniversaries badly.

This is because its history is built on divisions. To give an example, Titanic Belfast – a monument to the city's maritime heritage on the site where the RMS Titanic was built – was launched in 2012 as a showcase for tourism. Events marking the centenary of the ship's commissioning and tragic sinking in 1912 centred on a new museum and sought to capitalise on the success of the eponymous Hollywood movie.

However, many in the north did not share the view of the Titanic that was being whipped up by the marketeers. Catholics remembered that the liner was built in the East Belfast docks, a Protestant-majority area, and set sail amid "No Pope here" banners. This fact is even taught in Catholic schools. Titanic was a symbol of Unionist pride at the time of the Ulster Covenant, a landmark Protestant protest movement that laid the ground for the 1920 Act following the First World War.

For the 2021 campaign, the Northern Ireland Office – the Whitehall department that oversees the region – in tandem with the devolved, power-sharing government, has picked out notable Northern Irish figures. One of those chosen is Seamus Heaney, the poet and winner of the Nobel Prize in Literature.

On one level he is an obvious choice. On another level the use of his portrait is attempted appropriation.

During his lifetime, Heaney was scrupulous to avoid direct political interventions. It was a tough choice. Both sides tried to entangle him. But Heaney refused – to the point of snubbing known gunmen. The Oxford University Press included him in an anthology of best British poets. But Heaney was having none of it.

There is a common joke that when public figures such as George Best, Liam Neeson and Alex Higgins were winners, they were British. When they did something wrong, the headline writers made them Irish.

Heaney’s poetry grows out of the land, slow-changing traditions and the timeless myths that shaped him. The visitors' museum in his native village is tellingly named "Homeplace". That place is in Northern Ireland. But one of the state's founding fathers described it as a "Protestant Parliament and Protestant State". In other words, Heaney, a Catholic, had no part in it.

To the Oxford publishers in 1982, Heaney outlined his loyalties with a small bit of verse. “Be advised, my passport’s green/No glass of ours was ever raised/To toast the Queen”.

A Nationalist leader recycled the quote this month in protest against Heaney’s inclusion in the centenary campaign. Unionists were outraged. One leader pointed out that Heaney had toasted Queen Elizabeth at the state reception in Dublin Castle when she made a visit in 2011. In the context of the 1998 peace deal, Unionists see objections to the portrait of Heaney as contrary to the spirit of inclusiveness that it sought to foster.

British Prime Minister Boris Johnson set up the centenary commemorations after his first Brexit deal with Brussels undermined the Unionists. But his government is not neutral on the Union – a departure from the position of former prime ministers John Major, Tony Blair and David Cameron.

Theoretically, Northern Ireland could gain doubly from Mr Johnson’s successful effort to reposition the UK’s trading relationship with Europe. In contrast, the Union is also exposed in areas viewed as settled issues for the last quarter of its troubled 100 years.

Economic opportunities amount to just one of these issues. Culture is another. Loyalty is a third.

History is the ever-present factor. The binary choice that was offered a century ago has again been exposed as inadequate. The north and south are the products of that act. At some point, both will equally have to accept fundamental change in order to move on.

Damien McElroy is London bureau chief at The National