So...why are we killing Sarth again?

[Arcdelad]

As we crawled beneath wyrmrest temple the other day to vainly try and kill Sarth with one dragon still up, a lot of people started asking - what are we doing here? why are we killing this guy?

answers! not even loremaster supreme gren knows this! ha!

The story starts with Deathwing and the Nether dragons we all grew to love (or hate...man i hate dailies for rep)...lifted from wow-wiki:

Near the end of the Second War, the black dragon Deathwing traveled through the Dark Portal to Draenor. Believing the world to be a relatively safe haven for his offspring, he secreted away a cache of black dragon eggs. Following the war, Ner’zhul recklessly opened multiple portals on Draenor, and the magical stress tore the planet apart. The energies released in this catastrophe altered Deathwing’s eggs, resulting in the nether dragons: partially corporeal and partially ethereal dragons who possess the ability to shift between the astral and physical planes. Without Deathwing’s guidance, these otherworldly nether dragons are just now finding their own way among the blasted ruins of Outland.

One faction of nether dragons, named the Netherwing, were attacked by the Dragonmaw orcs of Shadowmoon Valley and many were enslaved by Zuluhed, including the female Karynaku (mate of Neltharaku) who was leader of the brood. Their son Mordenai wanders the Netherwing Fields seeking adventurers to help free his mother and eventually help the Netherwing escape enslavement.

Another brood of nether dragons, found at the Celestial Ridge in Netherstorm, is ruled by the corrupted crazed Veraku. Tyrygosa of the blue dragonflight seeks to defeat Veraku and take control of the brood for their own safety and to study their physiology.

Sintharia, a level 73 NPC in Shadowmoon Valley in BC, then creates a new breed of black dragonflight dragon using the nether dragons and black dragonflight dragons:

Sintharia was once the prime consort of Neltharion, who later came to be known as Deathwing. She gave birth to some of Deathwing's most despicable children, including the eldest, Nefarian, and his sister, Onyxia. After her mate's madness overtook him and the rest of the black dragonflight, the newly disfigured Deathwing attempted to mate with his consorts, causing Sintharia a great deal of pain and leaving behind scars and burn marks. Sintharia was the only mate known to have survived.

Approximately five hundred years prior to the opening of the Dark Portal, Sintharia attempted to bring down the Kirin Tor with a curse that left the wizards unable to use their magic. Her scheme was foiled in part by Korialstrasz, consort to Alexstrasza, and when Sintharia was defeated, most believed her to be dead. She survived, however, and forsook her mate and children, taking on the guise of Lady Sinestra, a name she came to use as a dragon as well.NotD 144

After the disappearance of Deathwing and the deaths of Nefarian and Onyxia, Sinestra reemerged hoping to continue her family's plan of creating a superior dragonflight to rule over Azeroth. Gathering up what shards of the Demon Soul she could find and Balacgos's Bane, Sinestra used these relics, along with the eggs of various flights she had collected over the centuries, and the captured nether dragon Zzeraku, to create the twilight dragonflight, one of the first of which was Dargonax whom she considered her child. Her old nemesis Korialstrasz, along with others such as Zzeraku, the blue dragon Kalecgos, the wizard Rhonin, Vereesa Windrunner, and the draenei priestess Iridi, put a stop to her operation. Sinestra was killed by Dargonax, whom had grown to hate his "mother".

Although she was defeated,

Although Sinestra and her creations were all slain, several of her unhatched twilight dragon eggs were taken from her lair in Grim Batol by Deathwing himself. Hiding in tunnels deep beneath Grim Batol, caverns older than any the dwarves had ever constructed, Deathwing safely stored the twilight dragon eggs and began his plans to perfect the new dragonflight, intending to erase the failures of his family and use the newest breed of dragon for his own designs.

So...we go into OS in order to slay a bunch of twilight dragon eggs before they hatch....why would that be bad? becuase:

Twilight dragons resemble black dragons, but they glow with a greenish, red, or amethyst light. The earliest twilight dragons created by Sinestra had the ability to feed off of magical energy, particularly enemy dragons. The later dragons, those raised by Deathwing, may have similar abilities.

To prevent a bunch of magic sucking vampiric dragons from hatching, we go in and kill Sartharian, and then presumably kill all the eggs. Why do it with some dragons left up? Becuase its there!

An excellent prequel to this storyline can be found in your local bookstore for $8 - "Night of the Dragon" by Richard Knaak...its the sequel (kind of) to "Day of the Dragon"...its a quick read too.