Responsibility for the Holocaust is the subject of an ongoing historical debate spanning several decades. Intentionalist historians such as Lucy Dawidowicz argue that Adolf Hitler planned the extermination of the Jewish people from as early as 1918, and that he personally oversaw its execution. Functionalists such as Raul Hilberg have argued that the extermination plans evolved in stages, as a result of initiatives from bureaucrats who were responding to other policy failures.