From "The Perimeter"
The Fleet had been on the alert for three decades.
Its thousands of ships cradled the Solar System in a heavily-armed, protective, electronic net, scanning the space lanes, ready to attack and erase the enemy--an enemy that, thirty years ago, had boarded and destroyed a merchant vessel ferrying bauxite from Titan to the aluminum refinery on the Moon.
Until that attack, the United Earth Directorate had been a world government in name only. Now the member nations were willing to give up some of their sovereignty--temporarily, of course--to combat a common enemy. They signed the Directorate's declaration of a global state of emergency and began to work together. And they worked wonders. The shield was built. The war had begun--a cold war against a cruel enemy that could turn up the heat at any moment.