Complex sentence: Thranduil first appeared in the prologue of', where he appears before Thrór, the extended edition also explains that the rift between the elves and the dwarves was caused when Thrór refused to hand over the White Gems of Lasgalen, which the Elvenking desired.
Split into simpler sentences: Thranduil first appeared in the prologue of', where he appears before Thrór. The extended edition also explains that the rift between the elves and the dwarves was caused when Thrór refused to hand over the White Gems of Lasgalen, which the Elvenking desired.