Ragnarök

"Thor will defy you and wage war against the Jotuns from now until Ragnarok."

- Loki to Odin

Ragnarok is a doomsday event in Asgardian culture.

History
After Sif's death at the hands of a Frost Goliath, Odin planned to use the Odinforce to revive her and prevent Thor from starting another war with the Frost Giants. Loki told him that Thor would defy him and wage war aginst the Jotuns until Ragnarok.