Thranduil first appears in the prologue of "", where he comes before the Dwarf-King Thrór. The extended edition of "An Unexpected Journey" explains that the rift between the Elves of Mirkwood and the Dwarves of Erebor began when Thrór refused to return the White Gems of Lasgalen, which was originally given to Dwarves of Erebor so that they would make a necklace for Thranduil's wife. Thranduil arrives with an army on the day the dragon Smaug destroyed Dale and Erebor, but leaves the surviving Dwarves to fend for themselves on seeing the might of the dragon and knowing what it could do to his forces. Thranduil's realm later face increasing attacks from the evil giant spiders from southern Mirkwood. In response to this growing threat, Thranduil adopts an isolationist policy and his territory is heavily defended.