The Demilitarized zone is a zone on the border that is heavily patrolled by Tundran Territories and Western Frontier military forces, it is litteraly a line right down the middle of the Tundran and Western Frontier borders, with a massive military strike force on either side, ready to attack at any moment.
It is also based off of the 38th Parallel, the border between North and South Korea in real life, with the "reds" or Tundrans being on one side, and the "greens" or Western Frontier being on the other, as with North Korea being the "reds" and South Korea, which is backed by America, being the "
It is non-existent in Battalion Wars 2, seeing how it was taken away when the Tundran's and the Frontier allied.