knuckle under vs succumb

knuckle under

verb
  • To yield or cooperate when pressured or forced to do so. 

succumb

verb
  • To yield to an overpowering force or overwhelming desire. 

  • To give up, or give in. 

  • To die. 

  • To overwhelm or bring down. 

How often have the words knuckle under and succumb occurred in a corpus of books? (source: Google Ngram Viewer )