The Nazis were not at war with the Jews - they decided to systematically wipe out a whole ethnic group of people, many of whom were their own citizens
Yet again, I'll recommend one of the greatest essays written on the topic of the Holocaust, Clive James' magisterial demolition of Daniel Goldhagen's "Hitler's Willing Executioners". Humane, informed, wonderfully written.
www.clivejames.com/evenaswespeak/hitler
and the equally essential postscript:
www.clivejames.com/evenaswespeak/goldhagen
Our post-Hannah Arendt imaginations are haunted by the wrong figure: for every owl-eyed, mild-mannered penpusher clinically shuffling the euphemistic paperwork of oblivion, there were a hundred noisily dedicated louts revelling in the bloodbath. The gas chambers, our enduring shared symbol of the catastrophe, were in fact anomalous: most of those annihilated did not die suddenly and surprised as the result of a deception, but only after protracted humiliations and torments to whose devising their persecutors devoted inexhaustible creative zeal. Far from needing to have their scruples overcome by distancing mechanisms that would alienate them from their task, their killers were happily married to the job from the first day to the last. The more grotesque the cruelty, the more they liked it. They couldn’t get enough of it. Right up until the last lights went out on the Third Reich, long after the destruction made any sense at all even by their demented standards, they went on having the time of their lives through dispensing hideous deaths to the helpless.