act of God vs difficulty

act of God

noun
  • Used other than figuratively or idiomatically: see act, of, God. 

  • An unforeseen occurrence beyond one's control, such as a natural disaster. 

difficulty

noun
  • That which cannot be easily understood or believed. 

  • Physical danger from the environment, especially with risk of drowning 

  • An obstacle that hinders achievement of a goal. 

  • The state of being difficult, or hard to do. 

  • An objection. 

  • An awkward situation or quarrel. 

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