What does Mein Kampf have to do with Jews and dehumanization?
As you probably know, Mein Kampf is the autobiography of Adolf Hitler and his statement of his political ideas and goals. In this book, Hitler talks a lot about his hatred for the Jews. The words that he uses in speaking about the Jews tend to portray them as less than human. Anyone who read his book and took it seriously would be influenced to hate Jews.
In the yadvashem.org link below, you can find many quotes from Mein Kampf that show Hitler's hatred toward the Jews. Looking at them, you should be able to see how the book tries to dehumanize the Jews. For example, Hitler portrays Jews as evil rapists who "defile" individual women but also the German nation as a whole.
With satanic joy in his face, the black-haired Jewish youth lurks in wait for the unsuspecting girl whom he defiles with his blood, thus stealing her from her people. With every means he tries to destroy the racial foundations of the people he has set out to subjugate. Just as he himself systematically ruins women and girls, he does not shrink back from pulling down the blood barriers for others, even on a large scale.
By saying things like this, Hitler uses this book as a way to try to make the German people hate Jews like he did.