Irish War of Independence: On "Bloody Sunday" in Dublin, the Irish Republican Army (IRA) assassinated a group of British Intelligence agents, and British forces killed 14 civilians at a Gaelic football match at Croke Park.

The Irish War of Independence, also known as the Anglo-Irish War, was a guerrilla war fought in Ireland from 1919 to 1921 between the Irish Republican Army and British forces: the British Army, along with the quasi-military Royal Irish Constabulary (RIC) and its paramilitary forces the Auxiliaries and Ulster Special Constabulary (USC). It was part of the Irish revolutionary period.

Bloody Sunday was a day of violence in Dublin on 21 November 1920, during the Irish War of Independence. More than 30 people were killed or fatally wounded.

The Irish Republican Army was an Irish republican revolutionary paramilitary organisation who waged a guerrilla campaign against the British occupation of Ireland in the 1919–1921 Irish War of Independence. It was descended from the Irish Volunteers, an organisation established on 25 November 1913 that staged the Easter Rising in April 1916. In 1919, the Irish Republic that had been proclaimed during the Easter Rising was formally established by an elected assembly, and the Irish Volunteers were recognised by Dáil Éireann as its legitimate army.

The Cairo Gang was a group of British military intelligence agents who were sent to Dublin during the Irish War of Independence to identify prominent members of the Irish Republican Army (IRA) with, according to information gathered by the IRA Intelligence Department (IRAID), the intention of disrupting the IRA by assassination. Originally commanded by British Army General Gerald Boyd, they were known officially as the Dublin District Special Branch (DDSB) and also as D Branch.