Why Dragons Went Extinct Before Game of Thrones, Explained

Dragons are one of the most important parts of Game of Thrones, but by the time the HBO fantasy series begins, the creatures have already been gone for generations. When Daenerys Targaryen receives three dragon eggs in Season 1, they are considered little more than ancient curiosities, and even Viserys Targaryen speaks of dragons as creatures that died long before he was born. Daenerys eventually changes things by hatching Drogon, Rhaegal, and Viserion, but their return raises an obvious question: how did they go extinct in the first place?