contention vs tug of war

contention

noun
  • Argument, contest, debate, strife, struggle. 

  • Competition by parts of a system or its users for a limited resource. 

  • A point maintained in an argument, or a line of argument taken in its support; the subject matter of discussion of strife; a position taken or contended for. 

tug of war

noun
  • A dispute between two parties, particularly an entrenched, back-and-forth dispute. 

  • A game or competition in which two teams pull or tug on opposite ends of a rope trying to force the other team over the line which initially marked the middle between the two teams. 

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