Great Migration

The Great Migration refers to a mass flight of Necropolis ghouls in the wake of the retaliatory attack by the Unity, following the death of Harry and his garrison at the hands of the Vault Dweller.

Background
Although ghouls have already traveled across the wasteland in limited numbers in the early 22nd century, the Great Migration occurred after 2162, leading to the previously concentrated population spreading out across New California and joining with other scattered ghoul individuals and small communities.

The Migration was triggered by the Vault Dwellers arrival in the Necropolis. Spotted by Unity spies, the Vault Dweller killed Harry and his team in order to secure the water chip, which resulted in the mutants retaliating against the Necropolis. Possessing the advantage of firepower and mobility, thanks to steam trucks they created, the Unity easily defeated the ghouls. It was a slaughter: The mutants' standing orders considered them expendable in the pursuit of any pure strain humans in Necropolis, and especially the Vault Dweller. The few ghoul survivors who did not flee the ruined city when the mutants arrived evaded the mutants by hiding. The sewers were a particularly good hideout until the mutants left.

Outcome
The flight resulted in ghouls scattering across New California. Major populations settled in Dayglow, Gecko, and Broken Hills. Ironically, the Great Migration allowed ghouls to thrive, with Dayglow eventually admitted into the New California Republic as a founding state, mutant protection laws passed in the early 23rd century, and ghouls serving in the New California Republic Rangers.

Appearances
The Great Migration is mentioned only in Fallout Bible, but its outcome can be seen in Fallout 2 and Fallout: New Vegas.