Here's a look at what you need to know about Northern Ireland. For many years, Northern Ireland has been split over the question of whether it should remain part of Great Britain or become part of Ireland.
Nationalists, who are mostly Catholic, would prefer to belong to a single, united Ireland. Most of its Protestants are determined to remain a part of the UK; they are called Unionists.
Northern Ireland's history has been marked by sectarian violence, although in recent years, its militias have begun working toward compromise.
In the past three decades, sectarian violence has left close to 3,600 people dead. The conflict is often called "The Troubles."
About Northern Ireland: Northern Ireland is one of the Home Nations of the United Kingdom, along with England, Scotland, and Wales.
Belfast is the capital of Northern Ireland.
Catholics make up 45% and Protestants, other Christian or Christian-related are 48%.
Political Groups and Militias: The Democratic Unionist Party (DUP)
Formed in 1971 by the Rev. Ian Paisley.
Mainly attracts support from working-class Protestants and believes Northern Ireland should be an integral part of the United Kingdom and opposes the Good Friday Agreement.
Vehemently anti-Catholic, and refuse to have contact with Sinn Fein.
Ulster Unionist Party (UUP) Led by David Trimble, the UUP is the main unionist party and has close links with the Orange Order, a Protestant fraternal organization.
It opposes any form of nationalism, which it views as exclusive and confrontational.
Formerly the Official Unionist Party, it formed the government of Northern Ireland from 1921 until 1972, when direct rule from London was imposed.
Social Democratic and Labour Party (SDLP) Its leader, John Hume, played a pivotal role in the peace process when he agreed to hold talks with Sinn Fein leader Gerry Adams and with the British Government.
The SDLP is the largest nationalist party in Northern Ireland.
The party attracts middle-class Catholic support as well as some working-class support, and aims to achieve the reunification of Ireland through democratic means.
Is a long-standing critic of all paramilitary groups and the British military presence in Northern Ireland.
Sinn Fein Northern Ireland's leading and oldest republican party .
Led by Gerry Adams.
Sinn Fein advocates a united Ireland free from British rule or a British presence.
The party's present form dates back to 1970 when Provisional Sinn Fein split from Official Sinn Fein, which became the Workers' Party.
The political ally of the Provisional IRA, Sinn Fein is a supporter of the Good Friday Agreement.
In 1986, a breakaway group, calling itself Provisional Sinn Fein, was formed which opposed IRA ceasefires and the peace process.
Irish Republican Army The IRA is the chief republican paramilitary group.