Germany, 1939–1945: The psychopaths from the Munich Beer Hall gained control of the reins of power of Nazi Germany and then of Nazi–occupied Europe. They held their mortal metaphysical enemy, the Jews, in their death grasp. The Nazis were apparently intent not just on murdering the Jews, but on “breaking them” prior, as well.
The logistics of setting up an apparatus murdering millions would turn out to be manageable for the “ever so efficient” Third Reich.
The harder part, that of neutralizing the hundreds of millions of Christian denizens of Greater Europe from protesting too strongly, had been taken care of for the Nazis in the preceding centuries leading up to the Holocaust by another institution, also masters of demonization, the Catholic Church.