Duel at the Rainbow Bridge

The Duel at the Bifrost Bridge was the confrontation between Thor and Loki upon Thor returned to Asgard from his exile on Earth. Loki intended to use the Bifrost Bridge to destroy Jotunheim and exterminate the Frost Giants, while Thor, incapable of allowing a genocide, had to battle his own brother to stop him.

Background
Loki learned that he was the son of the Frost Giant king Laufey, who abandoned him as a child to be found and raised by Odin, the king of the Asgardians. Since Thor was the "favorite son" of Asgard and destined to be its king, Loki felt rejected by both of his fathers. Loki invited Laufey to Asgard so he could kill Odin, who was incapacitated in his "Odinsleep", but Loki killed the Jotun King, doing something neither Odin or Thor would do.

Thor, in the Battle of Puente Antiguo, proved worthy of Mjølnir and to return to Asgard after his exile. He learned from Sif that Loki lied to him about their father's death.

Battle
Loki activitated the Bifrost to begin the destruction of Jotunheim by unleashing its full power. He explains that he only wanted to be Thor's equal in Odin's eyes, but now he desires the throne because he will have accomplished what no one else has done in destroying the Frost Giants. The two begin to fight. As Loki falls onto the Rainbow Bridge, Thor places Mjølnir on his chest, making him unable to move. Loki taunts Thor that what he has set into motion is unstoppable.

Meanwhile, Odin wakes.

Thor realizes that Loki speaks true and begins to hammer the Bifrost with Mjølnir. Loki tells Thor that if the Bifrost is destroyed, Thor will never see Jane Foster again. Thor continues to pound the bridge until it collapses. Both fall over the side to be caught by Odin.

Loki tells his adopted father that he did everything to impress him. Odin listens, but disappointment shows on his face. Loki decides to release his grip and falls into the abyss.

Aftermath
Loki is found by Thanos, who shows him the potential power of the Tesseract and gains Loki's servitude.

When Thor seeks to go to Earth because Loki is in Stuttgart causing a hostage situation, Odin must use dark energy to transport him.

With the Bridge destroyed, Marauders take advantage of the Asgardians' lack of transportation and plunder Vanaheim and other worlds.