Question: Denis O'Brien was a veteran of what conflict that led to the establishment of the Irish Free State?
Sentence (from "Irish Boundary Commission"): The 1921 Anglo-Irish Treaty, which ended the War of Independence, provided for such a commission if Northern Ireland chose to secede from the Irish Free State, an event that occurred as expected two days after the Free State's inception on 6 December 1922.
Relevant evidence: No