Northern Ireland was torn apart by three decades of violence between republican and unionist communities that ended with the Good Friday Agreement signed 20 years ago.

Here is an overview of "The Troubles" in which more than 3,500 people were killed.

Trouble starts

Violence erupts in 1968 when police use force against a peaceful Catholic civil rights demonstration in Derry.

The situation degenerates as Catholic meetings and demonstrations end in clashes with the police and Protestants.

In August 1969 violence inflames Derry and Belfast, and British troops are deployed.

IRA steps in

In 1970 the Provisional Irish Republican Army begins a campaign of bombings and shootings on the troops.

The violence is reciprocated by unionist paramilitary groups, driving a wedge between the communities.

Tensions rise in January 1972 after 14 people are killed on Bloody Sunday, when British soldiers open fire on a peaceful Catholic civil rights march in Derry.

Direct rule

London suspends the Northern Ireland provincial government in March, leading to decades of direct rule from the British capital.

In 1974 the IRA extends its bombing campaign to the British mainland with attacks on pubs in Guildford, Woolwich and Birmingham that kill about 30 people in all.

It also assassinates key British figures including Lord Louis Mountbatten, a cousin of Queen Elizabeth II, whose boat is blown up in 1979.

On the same day 18 British soldiers are killed in an IRA ambush.

Hunger strikes, bombs

A turning point comes in 1981 when IRA inmate Bobby Sands and nine comrades die on hunger strike at Belfast's Maze Prison where they are demanding political prisoner status.

Their deaths draw global sympathy for the nationalist cause.

In 1982 Sinn Féin wins its first seats in the Northern Ireland parliament. The following year Gerry Adams is elected party chief.

The IRA continues to strike England, attacking the heart of power in 1984 with a bomb at the Grand Hotel in Brighton as then prime minister Margaret Thatcher and her cabinet are there for a Conservative party conference. Five people die.

In 1992 and 1993 two massive bombings kill four people and cause major damage in the City of London financial hub.

Peace initiatives

An attempt by Conservative prime minister Edward Heath to establish a power-sharing executive founders in 1973.

Thatcher signs a new Anglo-Irish accord in 1985. In a major concession, it acknowledges the Dáil’s say in Northern Ireland's affairs, but it fails to win backing.

In the mid-1990s peace efforts again stall, leading the IRA to end a historic ceasefire in place since 1994.

It sets off huge bombs in London and Manchester in 1996. Two people die and the damage is enormous.

Good Friday breakthrough

In July 1997, after Tony Blair becomes Labour prime minister, Sinn Féin is offered a place at the negotiating table after the IRA declares a new ceasefire.

Following lengthy negotiations, the Good Friday Agreement is signed on 10 April 1998 between the British government, the Irish Government and the main Northern Ireland political parties, backed by the IRA.

It leads to a new semi-autonomous Northern Ireland with a power-sharing government between unionists and republicans.