What is the secondary cause of the holocaust
After WWI, Hitler blamed the Jews for Germany's defeat.
Hitler hated the Jews and thought they were bad and wanted them killed. I guess that would be the cause. There was no specific event that caused it, it just came from an idea.
Some German people's ancestors were the Huns, who came about 2000 years ago and mixed in with the Germans. And Hitler's opinions are just like the Huns.
Here's an idea read your history book