iron fist vs oppression

iron fist

noun
  • Ruthless and usually unrestricted control. 

  • Symbol of an army's tank or cavalry branch. 

oppression

noun
  • The exercise of authority or power in a burdensome, cruel, or unjust manner. 

  • The act of oppressing, or the state of being oppressed. 

  • A feeling of being oppressed. 

How often have the words iron fist and oppression occurred in a corpus of books? (source: Google Ngram Viewer )