Military action
The young human nations, Breland and Cyre in particular, were under growing threat from the goblinoid Dhakaanian Empire to the south. A young Cyrean prince warrior and his demi-god wife united the nations in a glorious war to push back the existential threat and, in doing so, forged a united empire named after the wife in honour of her glorious death in the decisive battle. So it was that The Union of Helleya, a coming together of the five human nations, was born and the Age of Fire commenced.