BELFAST (AFP) - Northern Ireland came into being on May 3, 1921, as Ireland became independent from Britain and was split between pro-Ireland nationalists and pro-UK unionists, who hold the most power. Here is a timeline of its history.
'The Troubles' begin
On August 12, 1969, "The Troubles" begin with sectarian fighting in Londonderry between Catholic nationalists and Protestant unionists. Two days later, British troops are deployed.
In December, pro-Catholic nationalist paramilitary, the Provisional Irish Republican Army (IRA) is formed.
British security forces start interning prisoners without trial in 1971 - 342 nationalists suspected of terror activity are immediately detained. Interrogation techniques used on prisoners have since been described as torture.
British soldiers shoot dead 14 at a peaceful nationalist protest in Londonderry on January 30, 1972, known as Bloody Sunday. British Prime Minister David Cameron later calls it "both unjustified and unjustifiable".
In March, the regional government in Belfast is suspended and Britain takes over "direct rule" of the province in an attempt to restore order.
Talks between British, Irish and Northern Irish leaders in December 1973 result in the Sunningdale Agreement, which pushes for a power-sharing government but the short-lived project is brought down a few months later by a general strike among unionists.
May 17, 1974, marks the deadliest day in The Troubles, with 34 killed in four bombings by unionist paramilitaries in the Irish capital, Dublin, and border town of Monaghan.
On Aug 27, 1979, 18 British troops are killed by the IRA in twin bombings at Warrenpoint - the deadliest attack on the army in the conflict.
Simultaneously, the IRA kills the cousin of Britain's Queen Elizabeth II, Lord Louis Mountbatten, by bombing his boat off the west coast of Ireland.
Republican prisoners begin a high-profile series of hunger strikes in 1982, seeking special political status. Bobby Sands is the first of 10 to die in the strikes, which generate international sympathy and are regarded as a propaganda victory for republicans.
Moves to peace
In 1985, the Anglo-Irish Agreement is signed, confirming Northern Ireland's status will not change without the consent of a majority of citizens.
Secret peace talks are revealed in 1993 between Mr John Hume, the leader of moderate republican party, the SDLP, and Mr Gerry Adams, the leader of the IRA's then political wing Sinn Fein. The talks laid the foundation for peace and Mr Hume would be awarded a Nobel Peace Prize for his role.
In April 1998, the Good Friday Agreement ends The Troubles. Paramilitaries agree to decommission weapons and Northern Irish residents can choose British or Irish citizenship, or both. A cross-community, power-sharing regional government is established.
In August, a car bomb in Omagh kills 29 people and two unborn children in the largest loss of life in a single incident in The Troubles. The bombing is carried out by a splinter republican group opposed to the peace process, but the scenes draw condemnation from mainstream republicans now devoted to peace.
The last British troops leave the province in 2007, ending a 38-year operation that remains the longest in UK military history.
Britain votes to leave the European Union in 2016, but 56 per cent in Northern Ireland vote to remain in the bloc.
Talks to deliver Brexit stall on Northern Ireland, with fears that new checkpoints on the border with EU member Ireland will be targets for dissident republican paramilitaries.
Unionists lose their parliamentary majority at the devolved assembly of Stormont for the first time in 2017.
Two years later, a British general election returns more nationalist than unionist politicians in Northern Ireland - another first.
On Jan 31, 2020, Britain officially leaves the EU. However, relations are frozen under the terms of a withdrawal agreement.
The Brexit transition period ends in January 2021 and a special "protocol" comes into effect for Northern Ireland, keeping it effectively inside the EU customs union and single market for goods.
Checkpoints to enforce this are erected at Northern Irish ports which some unionists decry as an "Irish sea border" undermining the position of the region in Britain.