Shang vs mainland China

Shang

name
  • an ancient dynasty in China 

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 Shang and mainland China occurred in a corpus of books? (source: Google Ngram Viewer )