The events of the Hobbit trilogy are set into motion many years earlier when the dragon Smaug decides to attack the dwarf settlement of Erebor. The dwarf king Thror had massed an incredible treasure in the mountain kingdom. The treasure and wealth of Erebor drew the attention of the great dragon and his wrath. Smaug first sets his sights on the village of Dale. Dale was a human settlement below the mountain of Erebor. Dale had grown wealthy due to trade that flowed out of Erebor.
Smaug begins his desolation of the village with bursts of fire. The town is incinerated and many of its inhabitants are killed in the onslaught. During the attack on Dale, one of the town defenders is able to shoot several of the special Black Arrows at the dragon. They do not kill Smaug but are successful in removing a scale from his beastly hide. The loss of this one scale will prove to be Smaug’s undoing.
When Smaug is finished with the human village, he focuses his attention on Erebor and attacks the kingdom under the mountain. Smaug bursts through the massive doors defending the keep and begins to slaughter the dwarves inside. The dwarves were quickly defeated and forced out of their kingdom. The treasure was now in the possession of Smaug. The loss of their home and their kingdom would mark the end of dwarf power.
In the coming movie The Battle of the Five Armies, Smaug will leave the mountain and attack the small village of Laketown. One of the unsung heroes of the town, Bard, still possesses the last of the Black Arrows. With the final Black Arrow, Bard will slay Smaug by hitting him where his scale was removed years earlier. Bard rids Middle Earth of one of its great dragons. The result of Smaug’s death is multiple parties attempting to make claim to the treasure the dragon left behind.
After the Smaug is killed the men of Laketown know that Erebor is unclaimed and they make plans to take the treasure. The humans from Laketown mass an army and march to Erebor to claim the treasure for themselves. The goal is to retain treasure to cover their losses caused by the great dragon. King Thranduil leads an army of elves to Erebor following the news that Smaug had been slain. The goal of the elves is to reclaim the treasure that they claim the dwarves stole for them.
The humans and the elves surround Erebor and Thorin is forced to summon the aid another dwarf kingdom in the Iron Hills. King Dain responds with an army of his own to come to the aid of Thorin. Finally, Gandalf warns the three factions of an incoming army of orcs. The orcs wish to destroy the dwarf kingdom and seize the massive treasure. The orcs now threaten all three armies and they band together to defeat the orcs.
The three allied armies are eventually joined by the giant eagles to become the fifth army involved in the battle. The allies are able to defeat the oncoming orcs and win the battle. All of these events are brought on by the death of the great dragon Smaug.