commanding officer vs warlord

commanding officer

noun
  • The officer in command of, and typically having ultimate authority over, a military unit. 

warlord

noun
  • A high military officer in a warlike nation. 

  • A local ruler or bandit leader usually where the government is weak. 

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