Sacking of Asgard

The Sacking of Asgard was a full-scale assault against Asgard by the Dark Elves during the second phase of the Dark Elf Conflict.

Background
In 2987 BC, the Dark Elves attempted to destroy the Nine Realms by dispelling the Aether through the Convergence, but were thwarted by an Asgardian army led by Bor. Malekith, the leader of the Dark Elves, escaped the battle with his lieautanant Algrim and various other soldiers under his command, and waited out the next 5,000 years in suspended animation.

Malekith and his kind were awakened when Jane Foster discovered the Aether after being warped to its location by the Convergence, and became its host. Taken to Asgard for treatment, Foster became a target for the Dark Elves. Malekith sent Algrim to Asgard under the guise of a Marauder, and instructed him to weaken the realm's defenses from within, allowing the Dark Elves to attack the realm with little resistance.

Battle
Captured by the Asgardians, Algrim was imprisoned in Asgard's dungeons, just as he had planned. Within his cell, Algrim activated a Kursed Stone, transformed him into a monstrous berserker, who immediately broke out of his cell, and proceeded to cause a massive riot by unleashing the other imprisoned Marauders. Lorelei was among the prisoners released. While the Asgardians were distracted with the Marauders, Algrim made his way to the royal palace's shield generator, disabling the shield and allowing the Dark Elves access to Asgard.

Despite Heimdall's attempts to stop their advance, the Dark Elves descended upon Asgard in a cluster of Harrow ships, which laid waste to the surrounding city and killing dozens of Asgardians. One ship, ferrying Malekith, crashed directly in the royal palace's throne room. Tracking Jane Foster to the king's chambers, Malekith found Foster being guarded by Frigga, Asgard's queen.

The two dueled briefly, during which Frigga seemed to have the upperhand, before their bout was interrupted by Algrim. Malekith then attempted to extract the Aether from Foster, only to find out that she was a holographic illussion created by Frigga. Enraged, Malekith ordered Algrim to execute the queen.

At that moment, Thor arrived and went into rage at seeing his mother being murdered. Firing a blast of lighting with Mjølnir, Thor disfigured Malekith, forcing him and the other Dark Elves to flee.

Aftermath
With the Dark Elves still looming over Asgard, the Asgardians prepared themselves for another battle. Thor, doubting that his people would be able to fare against the Dark Elves in their current state, attempted to convince Odin to lead the Dark Elves away from Asgard using Foster. Odin, blinded by sorrow and hate over the death of his wife, refused to listen, prompting Thor to carry out the mission himself.

After a series of intense altercations, Thor would eventually defeat Malekith on Earth during the Battle of Greenwich, avenging Frigga's death.