The event
The Dwarves of Khazad-dûm awaken a Balrog and abandon their greatest city.
Causes
The Dwarves’ deep mining in search of mithril released the Balrog beneath Caradhras.
Consequences
Moria becomes a place of Orcs and worse; the Longbeards are scattered for a thousand years.
Participants
Place
Sources
The Lord of the Rings · 1954–55
Three volumes: The Fellowship of the Ring, The Two Towers, The Return of the King.
The Silmarillion · 1977
Posthumously edited. Contains the Ainulindalë, Valaquenta, Quenta Silmarillion, Akallabêth and Of the Rings of Power.