Denis O'Brien was a veteran of what conflict that led to the establishment of the Irish Free State?
Irish Civil War: The Irish Civil War (Irish: "Cogadh Cathartha na hÉireann" ; 28 June 1922 – 24 May 1923) was a conflict that followed the Irish War of Independence and accompanied the establishment of the Irish Free State, an entity independent from the United Kingdom but within the British Empire.
i don't know