 He received his PhD (on the basis of published work) from Oxford Brookes University in 2002.Slim's writing on war is distinct for its determined focus on the civilian experience of war and the moral arguments he uses to justify the “civilian ethic” in armed conflict.His book, "Killing Civilians" (2007) used a historical perspective to establish “seven spheres of suffering” that are typical for civilians in war, and criticised a spectrum of “anti-civilian ideologies” in political and military policy that deliberately drive this suffering.