Warring States vs Yuan

Warring States

name
  • The era in ancient Chinese history following the Spring and Autumn period and concluding with the first imperial unification of China under the Qin dynasty (c. 475 BC to 221 BC). 

  • The era in ancient Japanese history of social upheaval and military conflict known as the Sengoku period that came to an end under the unification of the Tokugawa shogunate (c. 1467 – c. 1603). 

Yuan

name
  • The imperial dynasty of China from 1279 to 1368. 

  • A surname from Chinese. 

How often have the words Warring States and Yuan occurred in a corpus of books? (source: Google Ngram Viewer )