WARNING CONTAINS SPOILERS
Jack Vesailius became a super psycho and planned to dump the world into the abyss so he could "bring" it to his beloved Lacie and reunite with her. To do that he had to cut the chains that held the world together. He succeeded through the help of a Miranda Barma and Oz the B-Rabbit. However his plans were ultimately foiled by both Oswald/Glen Baskerville, who used all 5 of his black feathered chains (Raven,Dodo,Griffin,Jabberwock,Owl) to stop the breaking of the chains and Alice who killed herself so her sister (The Will) could not give Oz more power to break the chains once again, thus saving the world. However, it was too late for the city of Sablier, therefore Glen ordered the Baskervilles to slaughter all its citizens so that they would not become trapped in the Abyss and become Chains so in a way he was being considerate- hope that helps.