The majority of the island gained independence in 1921, following two years of conflict. But six of the nine counties of the province of Ulster chose to stay in the United Kingdom, eventually becoming the country of Northern Ireland.
In the late 1960s, the conflict between mainly Protestant unionists, who want Northern Ireland to remain part of the United Kingdom, and largely Roman Catholic nationalists, who want it to be reunited with the rest of Ireland, exploded into a political and sectarian war, known as the Troubles.
The three decades of ensuing violence between loyalists and the IRA claimed more than 3,000 lives, most of them north of the border. While the Good Friday Agreement of 1998 effectively ended the conflict, distrust remains between Catholics and Protestants.
Under the terms of the accord, groups on both sides dumped their weapons, and members of Sinn Fein, the political affiliate of the IRA, now work with pro-British politicians in Northern Ireland's power-sharing government.