The partition of Ireland on 3 May 1921, which created a devolved government in Northern Ireland, was intended to bring peace. Instead came discrimination, division and violence on both sides. In the second of a series of articles on the aftermath, an Irish historian looks at its disastrous legacy

It’s often difficult for those outside Ireland to wrap their heads around the fact that the great division in the politics of the Irish state has never been between right and left. Instead, its roots lie in a bloody feud within the Irish independence movement over whether the Anglo-Irish Treaty of 1921, which was to create an Irish Free State out of the United Kingdom but under the British Crown, was a betrayal of the Irish Republic or not.

The bitter conflict which resulted lasted from June 1922 to May 1923 and ended in victory by the pro-treaty forces. In some ways this civil war proved more significant than the independence struggle that had preceded it, because, in some ways, it has never ended. For up to nine decades it provided the organising principle of politics and society in the new state that had been created south of the border both locally and nationally, its legacy running through Irish life like letters through a stick of rock. The commemoration of the centenary of the start of the Irish Civil War – we are in the midst of a season of contested Irish centenaries – next year will be an uncomfortable affair, amplified by the irony that the two political parties formed by the partisanship of those years – Fine Gael (pro-treaty) and Fianna Fáil (anti-treaty) – are currently spancelled together in a loveless coalition government.