accede vs back down

accede

verb
  • To agree or assent to a proposal or a view; to give way. 

  • To become a party to an agreement or a treaty. 

  • To come to an office, state or dignity; to attain, assume (a position). 

back down

verb
  • To withdraw from a commitment or position. 

  • To take a less aggressive position in a conflict than one previously has or has planned to. 

How often have the words accede and back down occurred in a corpus of books? (source: Google Ngram Viewer )