cave in vs succumb

cave in

verb
  • To collapse inward or downward. 

  • To relent; to grant approval against one's initial will. 

noun
  • The act of relenting. 

  • The location where something has caved in. 

  • The act of something collapsing or caving in. 

succumb

verb
  • To overwhelm or bring down. 

  • To yield to an overpowering force or overwhelming desire. 

  • To give up, or give in. 

  • To die. 

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