regiment vs rule with a rod of iron

regiment

verb
  • To systematize, or put in rigid order. 

  • To form soldiers into a regiment. 

noun
  • A unit of armed troops under the command of an officer, and consisting of several smaller units; now specifically, usually composed of two or more battalions. 

rule with a rod of iron

verb
  • To rule with stern severity. 

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