Irish War of Independence
The Irish War Of Independence started the same day the first Dail opened which was the 21st January 1919. The start of this was an attack where two constables were shot dead in an attack on an explosives convoy in County Tipperary.
The Irish Volunteers changed their name to the Irish Republican Army (IRA) and became what can be best described as a guerilla force who then attacked the police and the military. The main purpose of these early attacks was to get as much guns and ammunition as they could lay their hands on.
To begin with this was a successful campaign for them and the republicans continued to grow and expand. De Valera had gone to America and received strong support there for the cause.
The British could do little to prevent these attacks and appeared lost as to a solution. It was also costing British tax payers £20 million a year. With some reluctance, Lloyd George the British Prime Minister came to the opinion he was not dealing with criminal activity, and was in face dealing with a popular and ever increasing movement.
His position became clear in that he two choice; negotiate an agreed settlement or wipe out the IRA and this republican movement.
The USA President Wilson, although no fan of Irish Republicanism was also putting pressure on Lloyd George to negotiate a settlement to what was termed, "The Irish Question." The Irish people were also looking for peace so a negotiated settlement was probably the only option left to Lloyd George.
I would now recommend reading about the First Dail.