Second Dark Elf Conflict

The Dark Elf conflict is a conflict that lasted for thousands of years. Dating back to 2987 B.C., when Malekith, the insane, genocidal leader of the Dark Elves, attempted to use the Infinity Stone known as the Aether to eradicate the Nine Realms. After the the Dark Elves were defeated by Asgardians led by the then-king Bor, Malekith and several others of his species went into hibernation. In 2013, during the Convergence, Jane Foster located the Aether and unintentionally attracted the attention of Malekith. A series of confrontations followed, spanning across all the Nine Realms, ending with Thor defeating Malekith at the Battle of Greenwich.

Background
In 2987 B.C., the leader of the Dark Elves, Malekith, planned to make all of the Nine Realms pitch-black using the power of the Aether. Soon the Asgardians heard of Malekith's plan, so to protect the Nine Realms, an army of Asgardians led by their king, Bor, went to stop the Dark Elves in the First Battle of Svartalfheim. Soon the Asgardians managed to take the Aether from Malekith. When the Asgardians began to get the upper hand in the battle, Malekith sacrificed everyone on the battlefield, even his own men. The remaining Dark Elves went into hiding and hibernated until the next Convergence.

Hunt for Jane Foster
Nearly five-thousand years later, the Convergence once again took place. Jane Foster, a human astrophysicist, came across a portal while studying the event, and accidentally warped herself to the Aether's hiding place. Jane unintentionally awakened the Aether, which possessed her body, using her as a host. Alerted by the Aether's activity, Malekith and his brethren immediately woke from their ancient slumber and followed the Aether's signal to Asgard, where Jane had been brought by Thor in an attempt to remove the Aether from her body.

Invasion of Asgard
To recover the Aether, Malekith turned Algrim into a Kursed, a Dark Elf super-soldier, and had him infiltrate Asgard. There, he posed as a prisoner and released various prisoners from Asgard's dungeons, and while the Asgardians were distracted by the prisoners, Malekith led a full-scale invasion of the realm. Heimdall attempted to halt the Dark Elves' advance by placing a force field around the royal palace, but Algrim lowered the field, and the Dark Elves swarmed the palace.

Malekith tracked Jane Foster to Odin's chambers, where he was confronted by Frigga, Asgard's queen. Frigga attempted to fight Malekith, but was restrained and subsequently murdered by Algrim. Enraged, Thor fired a blast of lightning that physically scarred Malekith's face, forcing him to retreat.

Return to Svartalfheim
Determined to avenge Frigga's death, Thor disobeyed the orders of Odin and, with help from Sif, Fandral, Volstagg, and Heimdall, released his war criminal brother Loki from his imprisonment so that he could help Thor and Jane Foster escape and lure Malekith away from Asgard. Hijacking a Dark Elf ship, the three fled Asgard and eventually found their way to Svartalfheim, where they were almost immediately confronted by the Dark Elves.

Despite their best efforts, Thor and Loki were unable to stop Malekith from taking the Aether from Foster's body, and were helpless to stop him from leaving the planet. Algrim stayed behind to deal with the Asgardians, and appeared to mortally wound Loki before being killed by one of his own Black Hole Grenade. After mourning Loki's apparent loss, Thor and Foster made their way back to Earth via another portal.

End of Malekith
Jane Foster and Thor returned to her flat in London, where they met with Darcy Lewis, Erik Selvig, and Ian Boothby. The group theorized that Malekith intended to unleash the Aether once again, and used a map left by early human civilizations pinpointing the peak of the Convergence to track the Dark Elf's location in Greenwich.

The group confronted Malekith in Greenwich, where he and Thor engaged in a brutal duel while Thor's human companions dealt with Malekith's minions using teleporation devices created by Selvig. Malekith, empowered by the Aether, proved to be more than a match for Thor. Their battle led them through various portals, transporting them to different locations like Svartalfheim and Jotunheim; the latter resulted in a Jotunheim Beast being transported to Earth.

The two combatants were eventually separated, and Malekith prepared to unleash the Aether unhindered. Fortunately, Thor arrived just in time to use Selvig's devices to transport Malekith away from the battlefield. Selvig used the devices on Malekith's damaged ship, teleporting it to Malekith's location on Svartalfheim; the leader of the Dark Elves was subsequently crushed and killed.

Aftermath
After the battle, Thor immediately returned to Asgard to confirm Malekith's death to his father. Odin commended Thor for his actions, which had saved the Nine Realms from decimation. What Thor didn't realize was that Odin was actually a disguised Loki, who had faked his death on Svartalfheim and had now usurped Odin's throne.

The Asgardians found Malekith's body on Svartalfheim and sapped the Aether from it. Deeming it too dangerous to keep, especially with the Tesseract already held in Asgard, they had it delivered to the Collector for safekeeping.

The wreckage from the battle was later cleaned by S.H.I.E.L.D., with the leftover pieces of Dark Elf technology recovered as harmful evidence.

The seductress Lorelei, who had been among the prisoners released by Algrim, managed to evade capture and made her way to Earth. She would eventually be hunted down by Sif, who allied with S.H.I.E.L.D. to capture Lorelei and return her to Asgard.