The majority of the jews killed in the Holocaust were not German, they were from all the occupied territories, most notably Poland.
Endlösung didn't kill anywhere near 1/4th of the population - it killed 1/3 %, and that fraction had already been systematically marginalised.
https://en.wikipedia.org/wiki/History_of_the_Jews_in_Germany...
https://en.wikipedia.org/wiki/The_Holocaust#Victims_and_deat...
Arguably step one had been occurring for hundreds of years before the Nazi's rise to power, but they really pushed the envelope.
What I find fascinating is I suspect for a great number of the leaders they really where just looking for something to vilify at the start and things just snowballed. It was only latter in the process as this huge segment of the population because less necessary that the idea of killing them showed up. Something like mass sterilization would have been as effective if there idea really was a twisted form of eugenics and they had been forcibly sterilizing people there and even in the US. However, while the initial idea may have been slave labor they kept sending so many people to these camps that they needed a 'solution'.
Pol Pot is an example of the other archetype of mass murder. He killed 1/4 of his country's population in 3 years in truly horrific fashion. But, in doing so he caused great harm to his own country's economy. What separates the Nazis is they efficiently eliminated large segments of the population without destroying society. It's horrific but also demonstrates at a somewhat visceral level that a large chunk of society is not that important. If 3/4 of the worlds bankers died tomorrow not much would change, if 3/4 of the worlds farmers died tomorrow there would be huge issues.