The IRA, the split, and the Anglo-Irish Treaty 

Opposition among Sinn Féin, Cumann na mBan, and the IRA to the Irish Free State’s dominion status within the British empire after the signing of the Anglo Irish Treaty led tothe Civil War, writes John Borgonovo

Refugees from Belfast arrive in Dublin, following the partition of Ireland into north and south.

In late 1921, Dáil Éireann plenipotentiaries in London negotiated a settlement with the British government which fell far short of Irish republican aspirations. 

The Anglo-Irish Treaty offered to a partitioned Irish Free State Dominion status within the British Empire rather than sovereign independence. The settlement generated intense opposition within Sinn Féin, Cumann na mBan, and the Irish Republican Army (IRA), which resulted in a civil war in mid-1922.