>>509278413 (OP)If we want to be as clear and accurate as possible... you're not wrong, but they start first with dehumanization. It's the minimum "you must be this tall to ride" qualification for any ethnic cleansing or genocidal program.
Hitler didn't set out to kill all the Jews. First, he wanted to deport them, and he tried. But deportation of six million people is an enormous logistical challenge and even with Germany's efficient and modern train network it was too hard. So they started containing in place. Ghettos, work camps, concentration camps, etc. But the thing is... even that's difficult. You have to feed them, water them, provide them with even basic clothes, etc. It's much easier to just kill them instead, and a "rational" (however morally depraved) next step.
It all starts from the perception that a group of people aren't actually humans but objects to be manipulated as such. Genocide is just a logical outcropping from this initial condition plus logistical failure.