The Anglo-Irish Treaty did not end the violence. The treaty effectively confirmed the partition of Ireland, setting up the Irish Free State in the south while Ulster remained part of the United Kingdom. Eamon de Valera had not been party to the Treaty and did not support it. When the Dail approved the treaty in January 1922, making way for provisional government under Michael Collins and Arthur Griffith, de Valera resigned and the nationalist movement split.
Many IRA officers were also against the treaty and established the Army Executive as the 'real' government. In April 1922 anti-treaty members of the IRA occupied the Four Courts in Dublin. The provisional government (in the process of building the National Army) was largely dependent on the IRA for policing and was unable to deal effectively with the escalating violence. In the same month the Cabinet decided to provide the provisional government with military assistance.
Winston Churchill, as Colonial Secretary, was increasingly angry about Collins' willingness to negotiate with de Valera. Collins made a pact with de Valera to form a joint government of republicans and pro-treaty members. At Cabinet meetings during May, Churchill argued strongly that the provisional government should be forced to take a stand against republicanism. This caused a rift in the Cabinet as the Prime Minister, Lloyd George, advocated a more liberal stance.
On June 16 1922, Ireland went to the polls. The pro-treaty representatives took 58 seats and the anti-treaty seats took 35. However, shortly afterwards republicans killed the Ulster MP Sir Henry Wilson, a prominent opponent of an independent Ireland, and kidnapped a general of the Free State Army. Collins responded by attacking the republican-occupied courts in Dublin.
The civil war progressed with increasing bitterness, but the anti-treaty faction did not have widespread support and the size of the National Army was increasing. The war ended in May 1923, but not before Eamon de Valera had been arrested and Michael Collins had been assassinated.