The dragons were bred by the noble houses to be extremely strong and smart, and eventually dragons, through selective breeding, were born with the intelligence of people. The dragons, with their intelligence, realized that they didn't want to be war beasts for humans anymore, and wanted freedom. The dragons at the Dragon Cathedral killed the humans there and took it over. They then flew to the king and demanded that they be given the cathedral as their own base, and wanted to be on the councils of kings and nobles. The king agreed, knowing that if he said no, they had no way to defeat all the dragons.
The dragons formed the Dragon Council, and sent one dragon to each of the noble houses to act as advisors. The dragons have a reputation for being extremely smart, wise, and powerful, being a welcome addition to the advisors of kings and nobles.