 The Grey Havens , an Elven port on the western shores , is attacked by the Corsairs of Umbar , allies of Sauron . The Dwarves , who have been reluctant to ally with the Elves , eventually decide to come to the aid of the Grey Havens . With the Goblins defeated and all of Eriador pacified , the Dwarven @-@ Elven alliance is tested by Sauron 's forces . Mordor 's overwhelming forces besiege the Lake Town of Esgaroth and the Dwarven city of Erebor . The Dwarven king Dáin leads a small group of Dwarves and men of Dale to defend their homeland and manage to eliminate the Mordor presence in Esgaroth but are forced to retreat back to Erebor to defend themselves against an overwhelming army led by the Mouth of Sauron . After a long battle against the Mouth of Sauron 's army , Elven reinforcements from Mirkwood led by the Elven king Thranduil arrive and save the Dwarves , defeating the Mouth of Sauron and his army . Elrond leads the first attack , but later , Thranduil , Glorfindel , Glóin , Arwen , and King Dáin all unite under the Dwarven @-@ Elven alliance for a final battle in Dol Guldur , the stronghold of Sauron in Mirkwood , aided by the Ents and Eagles . The Good forces and its three combined armies overcome the defenses and destroy the fortress , eliminating the last threat in the North . 
