Nazi ideology is not uniquely horrible, as other eliminationist rhetorics have existed and led to genocides of their own. Nor are their actions unique in numerical terms, as other authoritarian regimes have engaged in systematic genocides through famine etc. with similarly large loss of life.

But Nazism is unique in its combination of rhetoric and scale, and also in its instantiation within a highly developed society - politically, intellectually, culturally, and economically. Authoritarian horrors in less developed countries are still horrific, but it's not really surprising that an authoritarian can take over in a country where low standards of education are the norm and/or the mass of the population exists in grinding poverty and/or where long-standing tribal affiliations are suddenly exposed to drastic technological asymmetries.

Germany was a highly developed society at the leading edge of intellectual and industrial development. Numerous peer societies have also engaged in imperialism, and often in utterly reprehensible ways , but none of them industrialized genocide in quite the same manner that the Nazis did.