Metaphysical / Paranormal event
Due to fears of what would happen if another large-scale war were to occur, the Dragons decide to kill any of the Dragonkin they can find, despite them being their decedents.
The Dragons have gotten looser with their resolve not to interfere with humanity, and as the result of a few generational differences and close calls, Melanthos and Berliot decide that the magic is too dangerous to handle. Being the first to create a Dragonkin, Nernani feels uncomfortable about this, but goes along with it, even though half of the other Dragons have procreated since then. Only a fraction of the Dragonkin remains, escaping by the skin of their teeth, or by figuring out that their shared connection of theoretical Dragon blood put them at risk. A small group of them band together to survive the odds, and through one of them, Caleb's line is preserved.