Upon the calamity of the doom, the Valyrian Dragon Gods saw the decimation of their children. Except for a few that escaped with the Targaryen's and those that remained in the free cities, almost every majestic beast once ruled the skies and breathed fire, became nothing but bones and ash. A few unhatched eggs survived but were locked away in magical vaults.
This little security was all they could secure, as the Valyrians did not pay attention to the dragon dreams sent by their gods, except the Targaryen's. The warnings were even considered foolish by the powerful 40 families of the freehold. Thus all their effort could only claim a small victory.
Yet this victory was a calm before the storm. A few years after the doom, the free cities rebelled against their enslavers and killed both rider and their dragons. This chaos caused some alarms amongst the Dragon Gods of Planetos, especially Aegarax, the eldest among them. The extinction of the dragon species would upset the balance of the world, especially when Magic is necessary for its survival. The existence of Dragons was equivalent to magic. Magic was also needed to maintain the seals surrounding the imprisoned evils in the world. The Wall, Stygai and Sothoryos were the prisons of demonic beings that were maintained by magic, and without it, will unleash destruction far greater than the Doom of Valyria.
Shrykos, the goddess of transitions and doorways suggested to her brethren to call for the aid of those beyond their world. With the ability to traverse into different dimensions and worlds, she has met other divine dragons. These other gods hold dominion of their species in their own world. They would surely lend a helping hand given their predicament, since only 3 dragons belonging to the Targaryens' survived and most are already 100 years old.
Arrax, the ruler, is a bit hesitant to agree with his sister as those other gods may challenge and claim their divinity. But due to the urgency, they may yet indeed surrender. Seeing this dilemma, Balerion the God of Death made another suggestion. Instead of asking other gods for aid, why not call upon sentient dragon souls instead. They can either be alive or dead. Shrykos can open a gateway for those are still breathing, while Balerion can reincarnate the dead. He further added that these mortal dragons have no need of humans to rule them and instead have a kingdom exclusively only for the species.
The suggestion was a stroke of genius. Everyone agreed that Balerion's idea was the best way to move forward. They also liked the idea of sentient dragons ruling themselves exclusively. Thus Shrykos and Balerion started looking for dragon souls in their dominion that would be willing to live in their world