Which day in Irish history is called Bloody Sunday?

Bloody Sunday was a day of violence in Dublin on 21 November 1920, during the Irish War of Independence. Thirty-two people were killed or fatally wounded: thirteen British soldiers and police, sixteen Irish civilians, and three Irish republican prisoners.

The day began with an Irish Republican Army (IRA) operation, organised by Michael Collins, to assassinate the 'Cairo Gang' – a team of undercover British intelligence agents working and living in Dublin. IRA members went to a number of addresses and killed or fatally wounded fifteen people: nine British Army officers, a Royal Irish Constabulary (RIC) officer, two members of the Auxiliary Division, two civilians, and another man who is believed to have been an intelligence agent.

Later that afternoon, members of the Auxiliary Division and RIC opened fire on the crowd at a Gaelic football match in Croke Park, killing or fatally wounding fourteen civilians and wounding at least sixty others. That evening, three Irish republican suspects being held in Dublin Castle were beaten and killed by their captors, who said they were trying to escape.