While the Dragon of Hiroshima was the first, it was not the last. Mount St. Helens, the tsunami of Hawaii, the flood of the Yangtze....they were disasters, but no longer natural. Dragons rose, one or two for every great landmass and several more in the oceans. Lesser dragons arrived, small, cunning things of power and intelligence, but they feared the Wyrms as much as anything alive did. They were monsters as well, while the Wyrms were...other.
It was the fey who started integration. They had always been present, in all places, stories and folk tales, both human and monster. They forced cajoled, teased, and slowly brought together monsters and humans into larger communities. Oh, that made them no less dangerous or capricious. Even now the Elves slip into the edges of the less civilized areas, studying, gently making us aware of their presence, only to give gentle reminders and push us lightly towards unity.
So we arrive in the modern age, still fractious - even among ones own kind, the racial divides are strong, and this holds true of monsters and humans alike! - and still contentious, but with the knowledge that there are things the dragons, strongest monsters of all fear, and the Wyrms are not the only thing that is Other out there....