Asgard-Jotunheim War

"From a realm of cold and darkness came the Frost Giants,threatening to plunge the mortal world into a new ice age. But humanity would not face this threat alone. Our armies drove the Frost Giants back into the heart of their own world. The cost was great. In the end, their king fell, and the source of their power was taken from them."

- Odin

The Asgard/Jotunheim War is a conflict between the Asgardians and Frost Giants that took place in 965 A.D..

History
In the year 965 A.D. a host of Frost Giants from Jotunheim, led by their king, Laufey, invaded Earth at Tønsberg, Norway, in an attempt to bring about a new ice-age upon the people and to claim Earth as their own.

But humanity found its defenders in the form of the Asgardian army of Einherjar led by Odin Allfather, who defended the mortals of Earth and drove the Frost Giants back to their frozen home.

Odin pressed his attacked into Jotenheim and after a battle of great cost (Including his own eye, lost in battle on Earth), Odin defeated Laufey and took from him the source of the Frost Giants great power, The Casket of Ancient Winters.

Odin also secretly took home to Asgard a small Jotun baby, Laufey's son, who had been abandoned and left to die.

Aftermath
The infant Loki grew up as a brother to Odin's real son Thor, and Odin kept the boy's heritage a secret in the hope that he would one day come to end the enmity between the two races.