Complex sentence: While Bard and the Laketown survivors shelter in Dale, an elf army led by Thranduil arrives with supplies and aid, and forms an alliance with Bard, wishing to claim a necklace of white gems from the Mountain.
Split into simpler sentences: While Bard and the Laketown survivors shelter in Dale, an elf army led by Thranduil arrives with supplies and aid. Thranduil forms an alliance with Bard, wishing to claim a necklace of white gems from the Mountain.