Complex sentence: They were responsible for facilitating what was called the Final Solution, known since as HaShoah or the Holocaust, perpetrated by the SS in collaboration with the Reich Main Security Office, and the SS Economic and Administrative Main Office or WVHA.
Split into simpler sentences: They were responsible for facilitating what the Nazis called the Final Solution, known since the war as HaShoah or the Holocaust. It was perpetrated by the SS in collaboration with the Reich Main Security Office, and the SS Economic and Administrative Main Office or WVHA.