field marshal vs warlord

field marshal

noun
  • In certain nations the highest military rank, ranking below only the commander in chief; now essentially disused. 

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 field marshal and warlord occurred in a corpus of books? (source: Google Ngram Viewer )