Among scholars of the Nazi era, Hitler's role and relationship to the regime and the Holocaust has been a source of consternation and acrimonious historiographical debate. Biographer Ian Kershaw wrote that for historians Hitler was "unreachable" and that he was "cocooned in the silence of the sources". What Kershaw was referencing was the absence of any clear political directives accompanied by Hitler's signed authorization (primary source documents) regarding the atrocities carried out by his Nazi underlings. Given the abounding circumstantial evidence in Hitler's speeches, writing in "Mein Kampf", administrative meeting notes taken by subordinates and the recollections of those in or near his inner-circle, it seems that his political intention was for Jews, Slavs and other "enemies" of the Nazi state to be persecuted without mercy in lieu of how gradual the process actually developed. A debate between two primary schools of thought emerged about Hitler's political role in Nazi policy and the Holocaust. One is termed intentionalist, represented by scholars who contend that virtually all Nazi policies (including the extermination of the Jews) were resultant from Hitler's desires; whereas the other school, entitled functionalist/structuralist, consists of scholars who see the intensification of Nazi persecution policies due to power struggles within the Nazi government as his minions attempted to "interpret" their master's wishes, often acting autonomously.