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 centrality of what does Gallagher's definition uphold?