call to arms vs call up

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. 

call up

noun
  • An order to report for military service. 

verb
  • To select e.g. to a sports squad. 

  • To summon (someone) to report for military service. 

  • To retrieve from personal or computer memory. 

  • To call on the telephone. 

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