We live in a world in which events and actors not conceived of as posing an imminent danger during most of the twentieth century are now directly threatening human security. Critical infrastructures --from electric power grids to nuclear power plants, from water distribution systems to banks and air traffic control systems--are vulnerable to cyber attacks by state and non-state actors. Climate change threatens to disrupt people's lives and livelihoods, escalating disputes over access to key resources. Global inequality of income and wealth is undermining living conditions, especially in...