Each element (earth, water, air, fire, soul, and chaos) is represented by a selected leader. The leader, chosen by people of his or her element, has to make sure that their people do not go extinct (they will be extinct when no one can control their element).
Each leader minded their own business and would cooperate when needed. Any conflicts were settled by a one on one match between leaders. The winner would have their way in the matter. In this way, major casualties and unnecessary destruction were avoided.
However, a thousand years ago that changed.
The matter started as a simple conflict but escalated to something more.
At that time, the leader/king of air had commissioned a group of air users to wipe out a bandit group that was plaguing the common folk in his territory. The air users wiped the bandits out and were paid for their good deed. A happy ending, no?
No, it was not a happy ending. The bandit group was in fact a exploration group the the Fire King had organized so that he could obtain a detailed map of a trade route to the Air territory. It's just that the exploration group ran out of supplies halfway through a dense rainforest. When they finally made their way out they encountered a merchant caravan on the road and approached them to buy supplies. After a few weeks in the wild, they looked like barbaric bandits.
Their appearance made it so that the caravan misunderstood their intentions and attached them. After a fierce fight, both groups retreated and the merchant caravan safely made its way to town. There it spread the news that there was a bandit group near the town that should be eliminated. Worried, the townsfolk quickly requested that their king to send them aid.
This leads to the current situation: a fight between the air and fire users that usually coexisted harmoniously.
Of course, with the fuse being lit (or rather extinguished) , things only went downhill from there.