The Rage of Dragons

A Rage of Dragons, or Dracorage, was a periodic Realms-wide event that occurred when many dragons went on a collective, senseless rampage, destroying everything in their path. This periodic madness seemed to be tied to the appearance of the King-Killer Star, and could last for several tendays.
In Tiriande, the term "Rage of Dragons" generally refers to the Rage of 1018 DR, when Tiriande's allied nation of Cormyr, in the Prime Material, is ravaged by a series of dragon attacks. Then-King Olowarin Tiriande rides to its defense at the head of a Tiriandan army, helping bring an end to the siege.
Olowarin's calculated decision to aid Cormyr over several other, smaller trading partners facing similar situations throughout Toril helped gain him the title "The Grim".