Because of the winter war nature could no longer give as prosperous a harvest from the earth to the folk of Middle-earth as it did in the days before the Ivaldi clan became estranged from the Aesir. Before the winter war one sacrifice was offered to all the gods, Aesir and Vanir, but in increasing desperation Middle-earth implored the Vanir to bring back the summer and offered to make individual sacrifices to each of their patrons so that they would be given a good season of crops, fat herds and fruit on the trees.
So the most glorious of the Vanir, the wide -seeing witch Freyja set out to Asgard on what she considered to be a mission of parity with the Aesir. On her way to Asgard she walked through the frozen world and amazed Middle- earths folk with her powers weird, Men called her Heid, she could carve runes onto magic wands and had mastery of shapeshifting and occult prescience: she went into trances and could speak of the future. Upon her arrival at the hall of the High One Odin immediately asked her: Why have you come to Asgard, what do you ask of us?.
Freyja replied: The Vanir demand that individual sacrifices be consecrated to each of the gods because replenishing the earth has become much harder since Thiassi allied himself with the frost giants, even the Aesir have grown old because you can no longer eat Idun's apples. Middle-earth needs us to deliver abundance with the seasons, and when we do we should be regarded by the Aesir as equals.
All the witches of Middle-earth backed Freyja's demand.
Odin replied : All the gods, whether Aesir or Vanir are granted an equal part of every sacrifice from Middle-earth, great or small, noble or ignoble. Why should a sacrifice to each of the gods be considered as representing greater piety, would a mass sacrifice to fertilise the land with blood be a high and noble deed? The gods need sacrifices from Middle-earth but oft times they are just pleased for us to change fortunes. The gods require higher deeds from men, I made a huge sacrifice to create the world, but men do not yet know how to make higher sacrifices, for the folk of Middle-earth to try to make offerings to each of the gods would destroy too much of what we give to the earth, and destroy what Thiassi has not already frozen. We give as much as we can to men , we do not want to see it sacrificed as a petition for even greater harvests or favours, do the Vanir?.
Freyja knew Odin spoke the truth so she confronted him with what lay in the future: Terror of the gods I know where you left your other eye, you left it deep in Mimer's well, you sacrificed it so that you would be able to see everything with the other one but you still cannot see as far ahead as the Vanir. When Loki brought the treasures from the underworld he broke oaths and made the dark elves rage against heaven, from this crime more will follow, more solemn oaths will be sworn and then shamelessly broken without regret by the Aesir. You say that the world needs higher sacrifices from men, the Vanir see that Middle-earth needs peace because Loki, your brother has brought cold and war into the world by making the dark elves rivals amongst themselves. I see more wars breaking out in Middle-earth over a pile of gold and a cursed gold ring and worst of all I see three monsters coming, fathered by one of the Aesir; they will destroy all that you have created and all that you are trying to protect.
Odin was filled with uncertainty, then rage because Freyja spoke of the future and Odin did not know what the future held. The prophecy made the Aesir fear Freyja and the fear turned to violence, Odin ordered that Freyja be killed in the hall of the High One, so violating Asgard with death and blood. The gods took three spears and threw them at the Vanagoddess, all three spears hit their target and pierced her. Then they made a fire in the middle of the enclosure of Asgard and put Freyja's body onto the flames. The spear shafts burned and broke of in the inferno, then to the Aesirs fear and wonderment Freyja rose from the flames unscathed. The Aesir then grabbed three more spears and hurled them at the flame-defying Van, the spears all hit her and the gods burned her a second time with the same result, the spear shafts were burnt to ashes and she rose in the fire again.
Then they made a third and final attempt to kill her. After she had been burned thrice and speared nine times Freyja walked out of the fire towards the Aesir who were now all in awe of the witch and her indestructibility. Odin left the rest of the gods and went to his all-seeing chair on the mound Hlidsjalf above the world and looked out towards Vanaheim and saw the land, sea, waves, storm, sun and moon all bristling with rage because all of nature was seeking his head. From afar the Vanir had seen the Aesir's treatment of Freyja and they were advancing upon Asgard.
Out on the rim of the universe the nine giant women turning the handle of Mundilfori's world mill put the millstones into such a violent motion that the starry constellations above were disturbed and an earthquake flooded out the low lying regions of Middle-earth. Until the war of the Aesir and Vanir Mundilfori's mill had ground out fertile top soil, good will and happiness among men, but now, with the world in chaos and the gods attempting to slay Freyja in Asgard the mills workers started to grind out sand, salt and dust. Frost assailed the world as Thiassi's winter bit hard. Now Asgard came under siege from the Vanir.
The Vanir came up to the wall of the gods enclosure and called out to Odin: What have you done to Freyja our fair Sister
Odin did not answer, he raised his spear Gungner and slung it at the avenging host, war then broke out between all the divine clans.
Freyja's father Njord clove open Asgards gate with his axe, the Aesir defended the entrance. Njords son Frey the summer god; who brings warm rain, made a pact with Uller the winter god. Warm rain fell upon Asgards wall then Uller froze it splintering the stone, Frey then laid waste to the Aesir's fortification with a stags antler, the wall was ruined but the Aesir were not beaten. Their powers were declining since they lost Idun and her precious apples, but they fought back and neither side prevailed in the conflict, only the frost grew harder as the Aesir and Vanir destroyed each other.