Siberia vs demilitarized zone

Siberia

name
  • The region of Russia in Asia, stretching from the Urals to the Pacific Ocean. 

noun
  • A cold, inhospitable place or place of exile. 

demilitarized zone

noun
  • An area, often on a border between military factions, in which military forces and operations are prohibited. 

  • A subnetwork of a LAN, exposed to the internet or another untrusted network but firewalled off from the rest of the LAN. 

How often have the words Siberia and demilitarized zone occurred in a corpus of books? (source: Google Ngram Viewer )