befall vs happen

befall

verb
  • To happen. 

  • To fall upon; fall all over; overtake 

  • To happen to. 

noun
  • Case; instance; circumstance; event; incident; accident. 

happen

verb
  • To occur or take place. 

  • To do or occur by chance or unexpectedly. 

  • To encounter by chance. 

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