This is were i beleive the fight should be, because Cantha is based on ancient China and in Guild Wars 1 is was very naturery not counting the giant city(Keinege City). But for all I know Cantha proper could be all city by now.
Say the Dragon wakes up mad because its all city and no more natural land so it wants to take back the land that is now city, BOOM big reason for fighting Mordremoth.