Final answer:
Hitler justified the transition from expelling to exterminating Jews through the concept of ideological supremacy, based on beliefs of racial purity and the creation of a "master race," as per Nazi ideology.
Step-by-step explanation:
Hitler most likely justified his actions from expelling the Jews to exterminating them under the premise of ideological supremacy. The basis for this justification can be found in his beliefs about racial purity and the notion of an Aryan "master race" as outlined in his 1925 book, Mein Kampf, and further propagated by the Nazi regime. The ideology espoused by Hitler's government saw Jews and other minorities as inferior or "untermenschen" (under-people), where the extermination of these groups was deemed necessary for the purity and expansion of the Aryan race, a concept known as Lebensraum or "living space". This was also buttressed by warped interpretations of science and nationalism to suit the Nazi doctrine, which ultimately resulted in the genocide during the Holocaust.