Highlighting the potential for state and non-state actors to commit genocide in the 21st century, for example, in failed states or as non-state actors acquire weapons of mass destruction, Adrian Gallagher defined genocide as 'When a source of collective power (usually a state) intentionally uses its power base to implement a process of destruction in order to destroy a group (as defined by the perpetrator), in whole or in substantial part, dependent upon relative group size'. The definition upholds the centrality of intent, the multidimensional understanding of destroy, broadens the definition of group identity beyond that of the 1948 definition yet argues that a substantial part of a group has to be destroyed before it can be classified as genocide (dependent on relative group size).

In terms of failed states and non-state actors, the possession of weapons of mass destruction was an issue examined by which writer?