Hi AYE!
When imperial Germany went down to defeat in 1918, and Kaiser Wilhelm, the German emperor, was forced to abdicate, a popular theory that Germany had been stabbed in the back by the Jews took hold. Jews role, on the one hand, in the socialist and Communist movements that led revolutions in both Germany and Russia, and their prominence in international finance, on the other, led to dark theories about Jews lack of national loyalty, their treachery, and their degeneracy.
In Hitlers mind, all the groups that he saw as foiling Germany – Bolsheviks, socialists, social democrats – became identified with Jews, because indeed, Jews were so prominently represented among each of them. His political theories blended with increasingly technical racial theories that imagined the Jews, along with other groups like Slavs and Gypsies, as biologically inferior to Aryans, the white northern European race that pure Germans were presumed to belong to.