As WW2 progressed the Nazis attempted to ship the jews elsewhere. Sadly countries refused to accept these refugees.
Nazis then started to pile up Jews into Ghettos. Note that these Ghettos are almost identical to the Uyghur's current situation.
As the Ghettos started to fill up, the Nazis needed a plan on what to do as the ghettos started to reach capacity. Their decision is known as the "Final Solution" or death camps.
That's 2+ years after the start of WW2.