Why did Christians call Jews "spawn of satan" before the HOLOCAUST and then "Gods Chosen" afterwards ?

Sorry I can't answer for People that were Christians what 400-500 years ago...they are dead..they read what they wanted to the Jews have always been Gods chosen people...However I would say it is possible that the church leaders of the times back then said what they wanted for several reasons... the literacy rate was almost none..so people wouldn't have known any better ,because they couldn't check the facts they wanted to divide people because they could, to give them more control..power is an evil thing sometimes.