Well the tanks got rolling on September 1, 1939 when the Third Reich invaded Poland.
Some might point to January 30,1933 when AH was appointed chancellor by President von Hindenberg.
Others might site British PM Chamberlain’s acquiescence to AH’s demands at Munich in 1938.
Some might even cite the collapse of the DJIA in October 1929 which lead to the Great Depression which in turn lead to the rise of extremist parties in Germany and the collapse of the Weimar Republic.
Hitler should have never gotten a German citizenship