[1] Led by St John Brodrick, 1st Earl of Midleton, it split from the Irish Unionist Alliance on 24 January 1919 over disagreements regarding the partition of Ireland.
As a result, Midleton's wing of the party split from the IUA, establishing the Unionist Anti-Partition League that evening.
However, the majority of ordinary southern unionists remained with the IUA, which was left without effective leadership outside Northern Ireland following the split.
The group argued against Sinn Féin's policy of absenteeism from the British parliament, believing that it left Irish domestic interests without proper representation.
[4] The establishment of the Irish Free State in 1922 and the consequent decrease in the number of southern unionists resulted in the disestablishment of the League.