Attack on Jotunheim

"Do you realize what you've done? What you've started?" "I was protecting my home." "You cannot even protect your friends!"

- Odin and Thor The Attack on Jotunheim was an attempted attack on Jotunheim led by Thor after some Frost Giants managed to enter Odin's Vault and attempted to steal the Casket of Ancient Winters.

Background
"I think you’re right. About the Frost Giants, about Laufey, about everything. If they found a way to penetrate Asgard’s defenses once, who’s to say they won’t try again. Next time with an army."

- Loki

In 900 B.C, the Asgardians battled the Frost Giants on Jotunheim during the Asgard-Jotunheim War, ultimately winning the fight. Odin made a truce with Laufey, leader of the Frost Giants and confiscated the Casket of Ancient Winters. He also took an abandoned baby and adopted him, naming him Loki which was revealed much later.

During Thor's - Odin's biological son - coronation, the truce was seemingly broken when the Frost Giants entered Odin's Vault and tried to steal the Casket of Ancient Winters, but not before the Destroyer interfered and thwarted the theft. Thor, enraged then swore revenge on Jotunheim and gathered Loki, the Warriors Three and Lady Sif to accompany him on the journey to Jotunheim.

Attack
"At least make it a challenge for me!"

- Thor

Once they arrived on Jotunheim, they journeyed through the snow eventually making they way to Laufey. Thor questioned him about how his people were able to get into as gard. Laufey accused Odin of being a murderer and a theif and told Thor he was just a boy. He then allowed them to go, but a frost giant atangonized Thor by calling him a little princess. Thor immediately attacked the frost giant and a fence battle ensued between the Warriors three, sif, loki, Thor, and the frost giants as the fight continued Thor clearly enjoying the battle didn't heed the warning of his friends who told him to go as they fled Thor summed up a lightning strike taking out many frost giants. Then rushed to save his friends from a frost creature that Laufey summoned. Then Odin showed up and told laufey to end this now. Then laufey told him Thor sought this out, to which Odin replied to treat them as such then whisked Thor, loki, sif, and the Warriors three back to asgard. [Citation needed]

Aftermath
"Through your arrogance and stupidity, you've opened these peaceful realms and innocent lives to the horror and desolation of war!"

- Odin

Odin - enraged that Thor had selfishly attacked Jotunheim, sparking a war that Asgard is forced into and as a result, stripped him of his powers and banished him and Mjølnir to Earth.

Loki later revealed that he had informed a guard of their journey to Jotunheim, who in turn told Odin. Soon after Loki realized that he wasn't Asgardian, but biologically a Frost Giant, Loki raged as Odin fell into the Odinsleep.