Here how the dragon system works

There are the main elements 

Fire

Water

Nature 

Air

Darkness 

Light

These are the 6 kingdom ruled by Dutchesses or Dutchs. The 7 one is basically the kingdom that unites the kingdoms. A ruler rules that area and it can be of any species. Those who are half dragons or are kicked from there kingdom goes to live there. The roller of the 7 kingdom and the Duchesses and Duch of the kingdoms all share power