Dragons are competitive creatures. It is because of this that the four dragons remaining on the continent each claimed a kingdom for themselves. Having branched out and settled in their own kingdoms, the dragons are able to hold dominion over all the lives in a territory untouched by the other dragons. They use their environments almost to exhaustion, corrupting the land against its inhabitants.

Source and More information: Lore Update #6 – The Dragons of Bane and Flame

Author: indieDB.com