In Nazi Germany in the 1930's and '40's, Jews were marked with a yellow Star of David.  They were rounded up and taken to prison camps.  There they would be worked heartlessly until they were deemed no longer fit to contribute to the work, and killed.

The whole thing was about the science of work - scapegoating Jews for Germany's ills was clearly a front (though racial hatred is extremely effective for motivating unthinking idiots)...

If the Nazis killed a great number of Jews, it was because so many were dying of work, or were old and not able-bodied, et cetera.

Or they killed many Jews because the sheer number of Jews who were being pulled out of Nazi countries out of the momentum of idiot hatred, threatened to overwhelm their logistics and precious bureaucracy.  Extermination is a convenient oversimplification.

The Nazi regime was imploded after the required data had been gathered.  The Nazis were suckers, really.  All their backers actually wanted was to study a modern working scenario of slave labour.

The slave camps still exist, everywhere:

How naive it is to think, in our global world, that one must be on a particular side of a fence to be a captive...

How easy it must be, now, to mark a citizen, not with a star, or a heart or a rainbow, but with a bureaucratic flag that makes their career prospects fail, their medical tests get lost or mishandled, and their pleas to authority go unanswered...

How tragic and cruel it seems, on the surface, that vengeance is reserved for God alone.