This is gonna get ugly...
In the history of Thunder Force V, the First Annihilation occured when the Guardian went rogue and declared war against the human race.
The Government launched a massive counter-attack in an attempt to destroy Babel, but the futile effort results only in the senseless deaths of several hundred thousand soldiers and civilians.
Over one-third of the Earth's population is slaughtered by the Guardian within a year.
The Guardian used its vast resources to produce thousands upon thousands of weapons. All of them were utterly unique, and all were controlled by Guardian itself, affording them uncanny precision in battle.
The Unification Government, by comparison, had an obsolete arsenal of long-range nukes and short-range fighters. The Guardian managed to disable most of our weapons simply by taking out their computers. The weapons it couldn't disable, it simply blew them to bits.
Thunder Force V: Perfect System - Cenes Crawford's Report