reign of terror vs terrorism

reign of terror

noun
  • A period of brutal intimidation and violence by those in power. 

terrorism

noun
  • The use of intimidation or bullying tactics. 

  • The system of fear and intimidation put into place during the Reign of Terror in Revolutionary France around 1793-94. 

  • The use of unlawful violence against people or property to achieve political objectives. 

How often have the words reign of terror and terrorism occurred in a corpus of books? (source: Google Ngram Viewer )