Warring States vs mainland China

Warring States

name
  • 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). 

  • 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). 

mainland China

name
  • Also used other than figuratively or idiomatically: see mainland, China. 

  • The People's Republic of China, viewed as the general geographical region administered by the PRC in the aftermath of the Chinese Civil War (as opposed to Hong Kong, Macau, and Taiwan which are coastal and insular areas) 

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