Fall of Underland

The Fall of Underland was a largely mysterious brewing conflict that lead to a sudden climax in Narnian-year 2356.

Origins
The Queen of Underland, in seeking to control the Kingdom of Narnia through a puppet monarch, plotted an abduction of the young Narnian prince Rilian. A dark sorceress, the Queen transformed into a gigantic serpent, and in the year 2345, she ambushed Rilian and his mother, murdering the latter and imprisoning the prince for several years in her realm of Underland. She contained him using a device called the silver chair, which renewed a restrictive enchantment on him regularly.

Preparing for an underground invasion on the Narnian Kingdom by using hordes of magically enslaved Earthmen, her plot was foiled in 2356, before she could commence her attack on Narnia.

The Fall
A rescue party searching for Rilian, comprising Jill Pole, Eustace Scrubb, and Puddleglum, entered Underland in search of their lost prince and were able to support him in the destruction of the silver chair and in throwing off various other enchantments that the Underland Queen tried to use on them. When the Queen at last returned to her serpentine form, Rilian recognised her as the murderer of his mother and beheaded her as she tried to constrict him to death.

Immediately, the evil queen's death caused a chain reaction of magical spells throughout Underland that broke the Earthmen from their enchantments but also caused the underworld to implode. In thanks for killing the hated queen, the Earthmen led Rilian and the others out of Underland as it crumbled around them, allowing them to successfully escape the destruction. The Earthmen then returned to their homeland of Bism, which lain deeper toward the world's core. During the conflict, the Queen was the only known fatality; no Earthman casualties were ever confirmed during the collapse.