The One to Irk Them All: Sauron Shares an Unexpected Enemy With... Elves
Morgoth and Sauron were undoubtedly powerful beings who defeated many worthy foes, but they both had a weakness that may have played a decisive role in Sauron's ultimate defeat.
Two trees served as the sources of light in Middle-earth.
One of the mighty Valar created both and placed a silver tree in the north and a golden tree in the south, thus creating day and night.
These giant trees came to be known as The Lamps of the Valar.
Soon after, Melkor became aware of this creation and, possessed by jealousy, asked the giant spider Ungoliant (the spider that is the ancestor of Shelob, who appears in Peter Jackson's Lord of the Rings trilogy) to help him destroy the trees.
Morgoth destroyed both trees and allowed Ungoliant to suck out the rest of their life. Despite her best efforts, the tree-maker was only able to restore one flower from each tree.
The flower from the silver tree was used to create the Moon, while the flower from the golden tree was used to create the Sun.
The sun greatly hindered Morgoth and then Sauron, for the armies of the Dark Lords mostly consisted of trolls who turned to stone on the sunlight, and the orcs who were much weaker during the day.
Morgoth failed to completely destroy the trees, which led Sauron to try to somehow increase the effectiveness of his army during the day, and he created a new race of Orcs – the Uruk-hai.
These troops could easily cover decent distances on the run, could wait for the enemy for a long time in ambush, were skillful use of edged weapons, but what's more important – they weren't afraid of sunlight.
Although not only Morgoth and Sauron hated the sun, many elves did as well.
The alternation of day and night allowed humans to successfully develop agriculture, resulting in the rapid growth of the human race.
The sun had become a symbol of the strengthening of mankind and the transition from the Age of the Elves to the Age of Men.
In many ways, it was sunlight that prevented Sauron from conquering Middle-earth, and it is the sun that can be called the Dark Lord's most important and dangerous enemy.