Attack on Deltaheim was a surprise military strike by the Outsiders upon the Western Kingdoms. Outsiders intended the attack as a preventive action to cripple the Western Kingdoms by killing the five kings of the Western Kingdoms. Should the kings were killed in the attack, the existing world order would fall and chaos would inevitably descend.
Attack on the Palace
Teleportation Gate
Demon of Ruin

Aftermath
This attack led the alliance between Western Kingdoms and Hebrion Empire against the Outsiders.