Shoah vs ethnic cleansing

Shoah

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

ethnic cleansing

noun
  • The mass expulsion or killing of people belonging to one ethnic group by those of another. 

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