The Duel at the Bifrost Bridge was an attempt by Thor to prevent his adoptive brother Loki from using the Bifrost Bridge to destroy Jotunheim.
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 favourite 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.
Loki activated the Bifrost to begin the destruction of Jotunheim by unleashing its full power. He explained that he only wanted to be Thor's equal in Odin's eyes, but now he desired the throne because he will have accomplished what no one else has done in destroying the Frost Giants.