The Troubles: British forces began arresting and interning suspected Irish republican militants in Northern Ireland.

The Troubles were an ethno-nationalist conflict in Northern Ireland that lasted for about 30 years from the late 1960s to 1998. Also known internationally as the Northern Ireland conflict, it began in the late 1960s and is usually deemed to have ended with the Good Friday Agreement of 1998. Although the Troubles mostly took place in Northern Ireland, at times violence spilled over into parts of the Republic of Ireland, England, and mainland Europe.

Operation Demetrius was a British Army operation in Northern Ireland on 9–10 August 1971, during the Troubles. It involved the mass arrest and internment of people suspected of being involved with the Provisional Irish Republican Army (IRA), which was waging an armed campaign for a united Ireland against the British state. It was proposed by the Unionist government of Northern Ireland and approved by the British Government. Armed soldiers launched dawn raids throughout Northern Ireland and arrested 342 in the initial sweep, sparking four days of violence in which 20 civilians, two IRA members and two British soldiers were killed. All of those arrested were Irish republicans and nationalists, the vast majority of them Catholics. Due to faulty and out-of-date intelligence, many were no longer involved in republican militancy or never had links with the IRA. Ulster loyalist paramilitaries were also carrying out acts of violence, which were mainly directed against Catholics and Irish nationalists, but no loyalists were included in the sweep.

The Irish Republican Army (IRA) is a name used by various resistance organizations in Ireland throughout the 20th and 21st centuries. Organisations by this name have been dominantly Catholic and dedicated to anti-imperialism through Irish republicanism, the belief that all of Ireland should be an independent republic free from British colonial rule.