This thesis examines the political transformation and radicalisation of Ireland between the outbreak of the First World War, August 1914, and Sinn Fein's landslide electoral victory in December 1918. My hypothesis is that the repertoire of myths, memories and symbols of the Irish nation formed the basis for individual interpretations of the events of the Easter Rising, and that this interpretation, in turn, stimulated members of the Irish nation to support radical nationalism. I have based my work on an interdisciplinary approach, utilising theories of ethnicity and nationalism as well as social movements. With these theoretical tools, I go on to categorise the Easter Rising as a 'cultural trigger point': an event or series of events that creates a sense of agency and urgency in the face of what is perceived by the members of the nation as an injustice. These perceptions were reflected through the prism of Irish national myths, memories and symbols of the preceding three hundred years, including the Penal Laws and the Famine. My method here is to compare the condition of popular Irish nationalism before and after the Easter Rising in order to assess the impact of this event and its aftermath on the Irish nation. I trace, in particular, the impact of the Great War on cultural and religious nationalism and its role in the decline of moderate nationalism and the rise of radical Irish nationalism. The analysis of this process of radicalisation is accomplished through an examination of various contemporary sources such as personal journals, letters, Government Intelligence Reports, Episcopal letters, Diocesan Archives and Newspapers