repress vs rule with a rod of iron

repress

verb
  • To forcefully prevent an upheaval from developing further. 

  • To check; to keep back. 

  • To press again. 

noun
  • A record pressed again; a repressing. 

rule with a rod of iron

verb
  • To rule with stern severity. 

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