rule with a rod of iron vs strong-arm

rule with a rod of iron

verb
  • To rule with stern severity. 

strong-arm

verb
  • To bully; to intimidate. 

  • To coerce, to muscle. 

noun
  • A person who threatens or intimidates others, especially on behalf of somebody else; a goon or enforcer. 

adj
  • Bullying; extortionate. 

  • Coercive, employing force. 

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