Formation of Fenixia

Warring tribes fought over The Hollow Expanse, none of them able to claim ascendancy over the other for long. This conflict lasted generations and none of them were willing to forgo their claim to allow peace.

Invitation to talk

Horaeri, The First Emperor was the oldest son of one of the tribal chieftains and he wanted to find another way, to break free from the endless bloodshed. There were limited resources as it was, and the fighting depleted all of them without any real benefit.
He invited the sons of the other tribes to join him in the Shautane Grotto to offer tribute to their ancestors and to discuss how they could work together to bring peace to the region. With the arrival of the Radiant Phoenix and her renewal cycle starting over, they were all granted powers to manipulate the crystals lining the cave and imbued with the essence of the phoenix.

Takeover

With their ability to use the crystals to enforce their will, the group of them were unmatched by the other fighters. This led to them quickly deposing their fathers. Together the six of them sent messages to the other tribes - join and we will allow you the same priviledges as us to form your own family, otherwise we will force your descendants to serve us for generations.
The other tribes laughed at their messages, but didn't laugh long when the combined power of all the united tribes, along with the crystals wielded by their leaders, targeted them. They had no defense against this new power and quickly yielded.
Founding Fenixia
Once the other tribes were subdued, Haroeri, The First Emperor split the land and resources between those who had joined him. He wanted to form the tribes into a coherent entity which would never splinter into war again as each family would rely on the others for the other resources.
He made his capital on the banks of the river, designating areas for each of the families, and his own palace at the centre. He named this city Fenixia, the same as his Empire. From there he ruled over the whole of The Hollow Expanse from the mountains to the river, from the desert to the volcano.