The article charts the changing fortunes of the Catholics of Lisburn, County Antrim from 1914–22. It begins by exploring the establishment of a local battalion of the Irish National Volunteers and analysing Catholic recruitment to the war effort, before turning to the Easter Rising (1916), its aftermath and the bitter sectarian riots of August 1920, following the assassination of RIC District Inspector Swanzy. This murder in the centre of Lisburn led to days of violence and forced many of the town’s Catholics to flee. This paper argues that relations between nationalists and unionists in the 1914–22 period should be understood in the context of unionist beliefs regarding their communal safety and that territorial security is key to understanding the presence and form of violence in the town during the Swanzy Riots. Finally, some consideration is given to how this case study of Lisburn offers insight into understanding communal violence elsewhere in Ireland, during the wartime and revolutionary period.