At first, the Nazis merely wanted to round up all the Jews and exile them to the most inhospitable lands they could find. Madagascar was considered, as well as Siberia once the Soviet Union was conquered. In practical terms this would have been little different from gassing them outright; still, simply rounding up all the Jews and murdering them turns out to have been a last resort, embraced by people who truly felt a sincere belief that the elimination of Europe's Jews was a moral duty.
I'm looking for the quote but as I remember it,most were killed during a period of only 6 to 8 months.
Imagine the resources that could have been used for defense, ie; trains,personel,
only an insane hate could begin to explain it. The Islamists have it too.