The dead world from which Jadis comes is Charn. In The Magician’s Nephew, Charn is shown as a vast, ruined city and the capital of a world that has lost all life.
Digory and Polly reach Charn through the Wood between the Worlds and find empty streets, dried rivers, crumbling buildings, and a cold, dying sun. The Hall of Images contains statues or lifelike figures representing Charn’s rulers, revealing how the civilization declined from wisdom and prosperity into cruelty and tyranny.
Jadis was the last Queen of Charn. During a civil war with her sister, she used the Deplorable Word, an evil spell that annihilated every living creature in the world except the person who spoke it. Jadis then placed herself in an enchanted sleep, waiting for someone to awaken her.
Charn is often confused with Narnia because Jadis eventually becomes Narnia’s White Witch, but the worlds are entirely separate. Earth is Digory and Polly’s home, and Aslan’s Country is the heavenly realm associated with the end of the series. Charn’s destruction also explains why Jadis arrives in the wider Narnian universe as a uniquely dangerous survivor.