call to arms vs enroll

call to arms

noun
  • An appeal to fight or to engage in conflict. 

  • An appeal to undertake a particular course of action or to support a specific cause; a call to action. 

enroll

verb
  • To enlist oneself (in something) or become a member (of something) 

  • To enter (a name, etc.) in a register, roll or list 

  • To enlist (someone) or make (someone) a member of 

How often have the words call to arms and enroll occurred in a corpus of books? (source: Google Ngram Viewer )