The kingdom in The Eyes of the Dragon is Delain.
Stephen King’s fantasy novel is set in the medieval-style realm of Delain, where King Roland the Good rules with his queen, Sasha. Their sons, Peter and Thomas, become central to a succession struggle after the king’s death. The kingdom’s name is therefore not a character’s name or a location from another King story.
The main threat is Flagg, Roland’s magician, who schemes to destroy Delain and prevent Peter, the rightful heir, from taking the throne. Flagg frames Peter for Roland’s murder, while Thomas eventually becomes king under Flagg’s influence. The book’s plot follows the political and magical consequences of that conspiracy.
The Eyes of the Dragon was first published in 1984 as a limited-edition hardcover and later received a mass-market edition in 1987. It is often confused with King’s Dark Tower setting because Flagg appears in both stories, but Delain is the kingdom specifically associated with this novel.