In book 1 of The Dragon Lord Chronicles, Year of the Dragon Lord, a dragon named Song Li joined Argyll in attacking the Eldest. In book 4, Golden Dawn, we learn a little bit of why she did. Humanity bore a big share of the blame for its millennia-long war with dragons.
“We do not know how Lord Halfbeard died. The dragon they wounded was Song Li, whom you killed after Lochmaldie. We believe it was the final straw for her when dealing with humans. They had feigned distress, hoping to attract a nearby merchant ship. Instead, a dragon came to help, against her better judgment. But Ferdinand had been laying the groundwork for the treaty at Lochmaldie, and she agreed to give humans a chance. The pirates attacked en masse and managed to wound her in several places. She flamed the ship and flew away to heal. Many of the pirates survived by jumping ship and floating with debris to the shore. When the merchant ship came upon the wreck two days later, the pirates overpowered its crew. They killed most of them, but one of the few they let live managed to sneak overboard in port and tell the story. The Lochmaldie moot was only a week later, and by then Argyll had poisoned Song Li’s mind as much as the treachery of the pirates had.” -Cuthbert, dragon lore master and dragon lord
Copyright 2019 Miles O'Neal, Round Rock, TX Illustration from chapter 19 of Golden Dawn by Alli W. Ritchie