It starts with a feeling of being more like some people than others.
The comfort of being with people like you.
Then "them and us" become more clearly defined, more comforting in times of trouble.
Then "they" become the problem, they become other, they become less.
Then "we" feel the need to protect ourselves from "them", justified in demonising and dehumanising.
Our language starts to change, to reinforce, to exclude.
Laws are made - "We need to draw the line somewhere."
Crossing the line becomes life threatening.
Auschwitz is still there.
It looks like its last, sorry, occupants walked out yesterday...
I am currently reading Eli Wiesel's book "Night." If you haven't read it already, do so. And remember it every time you meet "other people" in the coming days and weeks.