Military action
From Scartia, an entire race of scaled, flying creatures invaded Terristra and made it their home during a particularly energetic Karkia. These creatures became known as Dragons.
As an invading horde, the Dragon race exploded into Terristra during the Karkia of the year 3564 BCC. They first emerged in the Highcrag Mountains, establishing the high peaks there as their staging grounds and eliminating any inhabitants before moving on to the rest of the continent. The horde was led by a huge red drake, with others of all colours (chromatic and metallic) forming squads of destruction that fell upon Dryholme. The Human inhabitants resisted heavily, bunkering down in Dryholme and mounting a defence. They immediately called for aid from the Stormchasers from Stormbreak, who managed to send enough magic users to prevent the city from being immediately destroyed. Once the initial invasion against the humans was less than total, the horde moved on to the rest of the continent. Over the next months, the dragons rolled over the native species, obtaining loyalty and service from all except the humans over the next few years after a lot of loss of life. After around a decade, the dragons attempted to move on to Ambion, but the races there had been forewarned enough to create more magical and physical defences, enough to dissuade the dragons from gaining a foothold on the continent. The attempted and failed invasion of Ambion continued for around 50 years before the dragons pulled back, mostly to Terristra. This failed invasion coincided with a large portion of the Dragon population apparently having a crisis of faith, and breaking from the main horde. Those known as metallic dragons started deserting the horde, making their way to isolated mountains, caves or underwater caverns and retreating from all contact with society. It is not known what precipitated this schism within the Dragon people, but it seems to continue to modern times. After the horde pulled back to Terristra, the humans wanted to use the momentum gained to attempt to reclaim Terristra as well. The other races, however, were reluctant to leave their shores, having barely survived the onslaught and wanting time to rebuild. Around 150 years after the start of the war, the Dark Plague was unleashed on Ambion. It did not change the opinions about participation in the reclamation of Terristra, and the humans lost enough ground that it was decided to abandon Dryholme and pull all inhabitants back to Stormbreak. Around this time, the dragons occupied Dryholme and started experimenting on the few human inhabitants that had refused to leave. This created a new race called Dragonborn who served their Dragon masters loyally and maintained the city, now renamed Scalemount. The war didn't end with a particular event or engagement, it just slowly petered out over the next few hundred years. Skirmishes kept the impression of war alive, but neither side mounted any further serious pushes into what had now become enemy territory. The humans declared the war over in 3051 BCC, and it is unknown whether the dragons also consider the war over, or if they even care.