This is not the edition I read, but the edition I read (in three volumes) was a library edition, so the dust covers may have been removed.
The Nazi party existed before Hitler took it over. After WWI, Hitler was employed as a spy, infiltrating and analyzing various dissident groups, and reporting back on them to his superiors. He found the Nazi party having regular meetings (often in the Hofbrauhaus in Munich). He dismissed them rapidly as a beer-drinking and political gossip society (if they hadn't been Bavarians, he might have used terms like 'kaffeeklatsch')--at least officially. But he came back to them privately, because he saw a potential to use them as a vehicle for his own ambitions.
The original members of the party welcomed him ambivalently. They didn't in fact agree with him on many matters. Many of them really were 'socialists', in accord with the original name later shortened to 'Nazi'. Many didn't agree with him on methods. Some started as skeptics, mutated into true believers, then (as often as not) ended up dead on the Night of The Long Knives. There were a few who managed to weather all the changes.
One of the main things that Hitler and the early Nazis did that was most effective is a practice called 'gleichshaltung'. Essentially they created a mirror state, with all the departments and ministries that the actual state had...BEFORE they ever had any political power. Thus, when the time came, they had ministers already lined up and trained, and bureaucratic engines primed and ready to be fired up.
This book is sometimes heavy sledding. A lot of it is dry. Some is terrifying, as when schismatics were purged. But it forms an essential basis for understanding how the Nazis did what they did. They didn't just spring fully armed from the Earth, like the army from dragon-s teeth in the old myth. In order to ward against a repetition, it's necessary to understand how it happened in the first place.