Complex sentence: In early 1942, Zyklon B emerged as the preferred killing tool of Nazi Germany for use in extermination camps during the Holocaust and claimed the lives of roughly a million people, most at Auschwitz.
Split into simpler sentences: In early 1942, Zyklon B emerged as the preferred killing tool of Nazi Germany for use in extermination camps during the Holocaust. The chemical claimed the lives of roughly a million people, most of whom died at Auschwitz.