The Strife of Fimbulwinter was an attempted invasion of Amusa by The Frostfell Empire from The Plane of Ice after they recovered The Ring of Winter's Wrath. The invading Frost Giants fought against and were repelled by members of The Tempest Brothers Expeditionary Company
The Tempest Brothers Expeditionary Company
Members of the Tempest Brothers Expeditionary Company had recently established themselves and founded the waystation of Tempest's Landing when they began to encounter planar frost giants in the Amusan wilds, far from their natural territory. After many encounters, some good some bad, the company forged a plan to combat the invading giants on three fronts to prevent their invasion from reaching the rest of Amusa.
Kalzivach
In their encounters with the Frost Giants, the company also encountered devils under the service of the Pit Fiend Kalzivach who was under standing orders from his master Mammon to prevent the Frost Giants from leaving the Plane of Ice. Since their goals were aligned, the company worked together with Kalzivach to defeat the Frostfell Empire.