At their first sitting in Dáil Éireann in Dublin, 21st January 1919, Sinn Féin:
On the same day:
The War of Independence had begun.
Michael Collins, the Irish Nationalist leader, had a spy network which meant that he knew what the British were up to in the towns anyway.
His 'Squad' of assassins eliminated anyone that Collins considered a threat.
In May 1921, the IRA attacked and burned the Customs House in Dublin. Attacking in 'Flying Columns' they ambushed the British and then disappeared into the countryside before the British could react.
The British sent in 'The Black and Tans' (a force of temporary special constables recruited to assist the Royal Irish Constabulary) in an attempt to put pressure on the IRA.
They burnt down and decimated Cork City, Limerick and Balbriggan.
In response to the killing of British intelligence agents in 1920, the 'Tans' killed 12 people and wounded 60 when they opened fire on a crowd watching a Gaelic Football match in Croke Park, an event that became known as 'Bloody Sunday'.
Later a group called 'The Auxiliaries', made up of army officers strengthened them.
In Britain, public opinion was critical of the Government over the conduct of their forces. On 11th July 1921 a truce between the Government and Sinn Féin came into effect to allow ceasefire talks to take place.