In Norse mythology, what event begins the chain of disasters leading to Ragnarok?

In Norse mythology, Baldr’s death begins the chain of disasters leading to Ragnarok.

Baldr is Odin and Frigg’s beloved son, famous for beauty, goodness, and near-invulnerability. Frigg obtains oaths from almost everything in the world not to harm him, but she overlooks the mistletoe. Loki discovers this weakness and gives the blind god Höðr a mistletoe projectile, causing Höðr to kill Baldr.

The gods’ attempt to restore Baldr fails when one being, often identified as Loki in disguise, refuses to weep for him. Baldr remains in Hel until after Ragnarok, when he returns to the renewed world.

Baldr’s death is not itself the final battle. It is a prophetic and emotional turning point, followed by further tragedy, including the punishment of Loki and the approach of Fimbulwinter.