Complex sentence: Sinn Féin was founded on 28 November 1905, when, at the first annual Convention of the National Council, Arthur Griffith outlined the Sinn Féin policy, "to establish in Ireland's capital a national legislature endowed with the moral authority of the Irish nation".
Split into simpler sentences: Sinn Féin was founded on 28 November 1905, when, at the first annual Convention of the National Council, Arthur Griffith outlined the Sinn Féin policy. That policy was "to establish in Ireland's capital a national legislature endowed with the moral authority of the Irish nation".