persecute vs rule with a rod of iron

persecute

verb
  • To harass with importunity; to pursue with persistent solicitations; to annoy. 

  • To kill many of one species of animal, with the intent of removing them from human habitats. 

  • To pursue in a manner to do harm or cruelty to; especially, because of the victim's race, sexual identity, or adherence to a particular belief. 

rule with a rod of iron

verb
  • To rule with stern severity. 

How often have the words persecute and rule with a rod of iron occurred in a corpus of books? (source: Google Ngram Viewer )