The conflict in Northern Ireland, which has killed thousands, has political and religious roots that are centuries old.
In modern times the conflict has centred on opposing views of the area's status.
Some people in Northern Ireland, especially the mainly Protestant Unionist community, believe it should remain part of the United Kingdom.
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Others, particularly the mainly Catholic Nationalist community, believe it should leave the UK and become part of the Republic of Ireland.
Since the 12th Century constant revolts challenged the often brutal British rule of Ireland, climaxing in the 1916 Easter Uprising in Dublin.
It sparked a chain of events leading to civil war and partition of the island.
In the south 26 counties formed a separate state, while six counties in the north stayed within the UK.
Unionists believe NI should remain part of the United Kingdom
Over successive decades the Catholic minority in the north suffered discrimination over housing and jobs, which fuelled bitter resentment.
The 'Troubles' begin
In 1969 Catholic civil rights marches and counter-protests by Protestant loyalists (as in "loyal" to the British Crown) spiralled into violent unrest.
British troops were sent in but soon came into conflict with the Provisional IRA (Irish Republican Army).
Loyalist paramilitary groups responded with a campaign of sectarian violence against the Catholic community.
As the situation worsened, Northern Ireland's parliament was suspended and direct rule imposed from London.
Violence on all sides
Throughout the 1970s, 1980s and early 1990s paramilitary groups waged violent campaigns to pursue their goals.
The IRA carried out deadly bomb and gun attacks in Britain and Northern Ireland that targeted police, soldiers, politicians and civilians.
Loyalist paramilitaries targeted Catholics in "tit-for-tat" killings.
Police and British forces tried to keep order, sometimes amid controversy, such as the alleged co-operation of some undercover units with loyalist groups.
Peace in sight
In the early 1990s negotiations took place between political parties and the British and Irish governments.
After several years of talks IRA and loyalist ceasefires held and in 1998 the "Good Friday" agreement was signed.
It set up a power-sharing executive, with ministerial posts distributed by party strength, and elected assembly.
The deal was backed by voters in referendums in Northern Ireland and the Republic, which scrapped its constitutional claim to the north.
Problems remain as devolution has been suspended several times since it began.
It was last suspended in October 2002 over allegations of a republican spying ring at Stormont. The case against the accused later collapsed and one of the defendants was revealed to be a British agent. He was found shot dead in April 2006.
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In September 2005 the arms decommissioning body confirmed the IRA had put all its weapons beyond use. But unionists said they remained sceptical without any photographic proof.
A deadline was set by the government for the Northern Ireland Assembly to resolve its differences and resume power-sharing by 24 November 2006.
However, as politicians met that day to hear if the DUP and Sinn Fein would indicate their candidates for the first and deputy first minister jobs, loyalist killer Michael Stone burst into Stormont.
He was later charged with attempting to murder Gerry Adams, Martin McGuinness and two security guards.
Northern Ireland Assembly elections were held on 7 March and the DUP and Sinn Fein emerged as the biggest parties.
Several weeks later, Ian Paisley and Gerry Adams agreed an historic power-sharing deal, naming 8 May as the date when devolution returns to Northern Ireland.