History is replete with unprecedented waves of incursions by non-state actors into sovereign state and in the spirit of self-preservation and self-defence these aggrieved states have mounted peremptory campaigns into other neighbouring and distant states to rid the errant non-state actors of the capacity to carry out future attacks against them and to restore the reality of national security within their territorial boundaries. This article seeks to analyse the extent of a states right to defend itself against non-state actor and in the course of this analysis issues like the threshold to justify the sovereign state offensive action and the necessity for self-defence will emerge. These issues will be analysed in line with the principles of international customary law, conventional law, opinion juris and recent state practices.