The Unmanned Attack was accidentally set off by a Kisaragi research team exploring an ancient weapons facility, despite attempts to prevent it. The resulting devastation destroyed much of the world's infrastructure, and also did considerable damage to most cities and organizations. It forced the three major corporations, Kisaragi, Crest Industries, and Mirage, to pool resources to form the Alliance and also resulted in the closure of the Ravens' Ark.
A second attack would occur some time during the events of Armored Core: Last Raven, depending on the route taken, and devastated the world again. With the destruction of the Internecine, it is assumed that all remaining Unmanned Suicide Weapons were deactivated.
- Although it is not ever stated, during the start of the attack (the end of nexus) it is implied the raven (the player) is killed by the suicide weapons.