bring to heel vs mitigate

bring to heel

verb
  • To cause to act in a disciplined manner. 

  • To compel someone to obey; to force someone into a submissive condition. 

mitigate

verb
  • To reduce, lessen, or decrease; to make less severe or easier to bear. 

  • To downplay. 

How often have the words bring to heel and mitigate occurred in a corpus of books? (source: Google Ngram Viewer )