Asgard is the ancestral home of the Asgardians, mighty warriors of myth and legend. It is a demesne of potent and ancient magics and rich history. It is the home of Odin and the Aesir, and they have been the temporal guardians of Earth for millennia.
Asgard is a rare demesne that protrudes into reality. The name is given both to the Kingdom of Asgard and the Nine Realm of Yggdrasil it claims, as well as to the Golden City where the royal palace and bulk of the population reside.
It can be accessed by stepping through the branches of Yggdrasil, coasting through the Astral Realm, or sailing into the depths of space. This balance, existing across multiple realities, is part of what keeps Asgard stable and safe from many challengers.
History of Asgard
When the Asgardians first rose to power, the Norns warned the Elder Gods that Asgard would lead to the doom of Yggdrasil and the destruction of the Demiurge. The encroachments of the Kryptonian Hegemony were so intolerable a threat, though, that Oa convinced Gaea to persist with the creation of these legions of warriors. As a fail-safe, Asgard was trapped in a cycle of cataclysmic reset. Every five thousand years, conflagration would wrack The Nine Realms. Surtr would destroy Asgard's kingdoms and return to the fires from when he came. The ideologues of Asgard-- Buri, Thor, Odin, Loki-- would die and be reborn, over and over, memories manipulated and none the wiser for it. Eight full cycles of this reset, this ragnarok, occurred, with rare echoes persisting from one iteration to the next.
During these early years, Asgard clashed heavily with the Kryptonian Hegemony and the Kree Empire. Their warmongering proved the concerns of the Norns to Oa, and the cycle of death and rebirth persisted for millennia.
In 15,000 BCE, war came to the Earth as an army of Celestials invaded. King Thor led the armies of Asgard as the vanguard force against the Celestial war host. In the 11th hour, Merlyn the Magician and the Vishanti channeled the cosmic might of all the realms of Yggdrasil and annihilated the Celestial invaders. Bare minutes later, with the Demiurge weakened to the point of death, Morgana Le Fay used the long-lost Cosmic Cube and summoned dread C'thulu. The ancient Old One destroyed not just Atlantis, but forced the Demiurge to expend the last of its life force to contain the monstrous entity. Ancient chains set on Surtr lost their strength and the fire giant strode across Yggdrasil to deliver the death blow to Asgard's realms. Such was the force of this blow that Heven was irrevocably sundered from the rest of the Realms and lost forever. This 'true' Ragnarok, the End of Days, had come as the Norns predicted.
Following the silencing of the Demiurge, Asgard was one of the first realms to recover their potency. The Ice Giant Ymir and the Elder God Gaea spawned a great warrior, named Buri. Buri, The First, would become a New God and Father of the Asgardians. Buri fought Surtr and chained the fire giant to his ancient throne once again, unaware of how many times the Ragnarok Cycle had played out this scene.
His three sons-- Bor, Njord, and Mimir, would follow in his footsteps. Njord fathered the Vanir, becoming the ruler of the lands of Vanaheim. Mimir became a sage, itinerant and ever-wandering in search of knowledge. Bor would serve as the strong right arm of Buri's armies, projecting their military might to conquer The Nine Realms. Buri's victories would cement their reputation across the cosmos.
Four thousand years after the collapse of the Demiurge, the Asgardians were warring across the long lost Nine Realms, those demesnes closest to Midgard. Bor discovered that his father had found the unoccupied dimension called Asgard and refused to allow his people to settle it, wishing its power for himself. Challenging his father to combat, Bor was victorious. Buri was banished and Bor became King of the Asgardians. Using his mighty magic as ruler of Asgard he created a golden city floating in the stars. Those who followed him to that land became known as Asgardians. Their cousins, descendants of Njord, would occupy Vanaheim, while refugees from the Fae realms would settle nearby Alfheim and Nidavellir-- becoming the Light Elves and the Dwarves, respectively.
Bor grew weary of warfare and slaughter, and when The Nine Realms were conquered to his satisfaction, he handed the throne to his son Odin near the terminus of the Hyborean Era approximately 3000 BCE. Brash and warlike, young Odin accelerated the conquest of other realms. He appointed Hela the Goddess of Death, setting her over Helheim and bidding her to gather souls aggressively as possible to ensure Asgard's power would not wane.
War of the Worlds
Asgard's warlike expansionism conflicted with the growing Kree Empire and even regained the attention of Oa. The long-lived manipulators turned to a relatively young race on the planet Thanagar, a planet with a strong martial tradition. Their tremendous reserves of the rare Nth Metal made a formidable counter for Asgard's forces.
Oa boostrapped Thanagar into a spacefaring race, then simply ensured Asgard and Thanagar would find some common territory to fight over. A crushing defeat at the hands of the Hawkmen finally tempered Odin's battle lust. He went to the Norns, seeking wisdom, and in exchange for his eye he was given profound and secret knowledge about the need for Asgard, the history of Ragnarok, and the destiny of his people-- and his future sons.
He turned to domestic concerns, and began building an empire on the bones his father and grandfather had lain down. A political marriage with Freyja of the Vanir helped Odin build a new peoples: the Aesir. The Valkyrja were formed as an elite commando unit, for both special tactics and command on the battlefield; they were also meant to act as psychopomps to ensure as many souls as possible could be brought to Helheim's frigid shores.
In 500 CE, the Frost Giants and their mighty Ice Giant forebears attempted to invade the frigid northern realms of Midgard. Odin's armies swept down from Asgard and forced them back. The battles raged for most of two hundred years, during which time Frejya bore Thor, Odin's first son. Bare weeks later, Odin found an infant Loki on the battlefield and claimed him as his second-born. With the Nine Realms safe and secure again, the All-Father set himself on Asgard's Golden Throne and sent his sons out into his stead to keep the realms of Yggdrasil safe.