Who is The Nazis from The Madonnas of Leningrad: A Novel and what is their importance?

In the early-to-middle years of the twentieth century, the government and military of Germany was run by the Nazis, a group of ultra-nationalist, ultra-conservative, and ultra-violent men and women who believed in the inevitable, god-given superiority of the German people. Led by the deranged Adolf Hitler, the Nazis overran much of Europe, their cruelties and atrocities to both people and places becoming legendary in the annals of war crimes committed throughout history.