Shoah vs night of the long knives

Shoah

name
  • The systematic mass murder of six million Jews perpetrated by Nazi Germany shortly before and during World War II. 

night of the long knives

noun
  • A purge, in which opponents of a regime or political party are killed or removed. 

How often have the words Shoah and night of the long knives occurred in a corpus of books? (source: Google Ngram Viewer )