In the BBC's 1997 documentary 'The Nazis: A Warning From History', the rise and fall of the Nazi regime is examined. Another insightful analysis is Timothy Snyder's 2015 book 'Black Earth: the Holocaust as History and Warning'.
From these sources we gain an important insight into the character of the Nazi regime, and how fundamentally different their thinking was. This cannot be stressed enough, that you cannot merely think of the Nazis and Hitler as just nationalists, or just antisemites.
Their behaviour contrasts with the behaviour of antisemitic nationalists, like Antonescu's Romania. Romanians helped to exterminate 300,000 Jews... and then completely reversed their policy, because Antonescu's primary objective was national supremacy, and not racial supremacy inclusive of a life or death struggle against international Jewry.
The Nazis, and Hitler in particular, were racial anarchists. Snyder goes into this in detail, but the gist is this: Hitler believed that the natural way of things is violent struggle between races, allowing the superior to be superior. Hitler also believed that the legal and philosophical evolution of civilisation, from Christianity to ethics and law, were created and maintained by an elaborate global Jewish conspiracy to alienate people from their natural struggle. To enable allegedly inferior Jews to keep allegedly superior Germans under control, and pervert the natural order of things.
Consider how the popular German response to their losing the First World War was a 'stabbed in the back' myth. Allegedly, it was Jews that were responsible for selling out, and if only they had continued fighting they would have achieved victory (which was completely fanciful thinking). The Germans then had to suffer the treaty of Versailles, again blamed on Jewish elements.
Of course it doesn't make sense to continue a genocide when those resources could otherwise be allocated to a war effort, especially when the war is going badly. But that rational response is a distinctly un-Nazi one.
To the Nazis fighting in the east, there was little distinction between efforts to exterminate Jews, and fight Russians. They sincerely believed that the liberal regimes in Britain and America, along with the Communist regimes in the USSR, were two sides of the same Jewish coin, and were both ultimately controlled by a giant Jewish conspiracy.
Furthermore, it is important to add that the Nazis had become complacent and optimistic after swift conquests in Poland and France. The Nazis believed sincerely that an attack on the Soviet Union would result in another swift victory. They perceived the USSR's apparent strength to be merely a facade, part of an illusory system of Jewish conspiracy and control. But when the superior German people were sent to knock the facade down, the whole house of Judeo-Bolshevism would collapse. This idea initially seemed correct as the surprised and unprepared Soviet army struggled to cope. But as the war turned against them the delusion proved problematic, which for most committed Nazis served only to increase their denial and zealotry.
Most Nazis regarded the war, especially against the Soviets, not simply as a war between nations, but as a war of annihilation to be fought to the bitter end. Emboldening this fervour was a sincere belief in German racial supremacy, and implicit in this is the belief that they could not lose against a racially inferior foe.
To conclude, as Snyder said in an interview on the subject:
At the end of the war, Hitler said, ‘Well the Germans lost, that just
shows the Russians are stronger. So be it. That’s the verdict of
nature.’ I don’t think a nationalist would say that.