bring to heel vs enslave

bring to heel

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

  • To cause to act in a disciplined manner. 

enslave

verb
  • To make subservient; to strip one of freedom; enthrall. 

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