From the introduction: In 2065, Earth lies in ruins, largely abandoned in the aftermath of a one sided conflict between humans and the mysterious entities called the “Phantoms”. 34 years ago, the Leonid Meteor struck the planet, and from the smoldering crater, alien creatures known as the Phantoms spread out across the planet. First contact with the alien species proved fatal to humans, and no attempt at establishing a means of communication had any effect, the Phantoms ignored the humans and continued to spread from the impact site. Unable to contain the Phantoms, humans across the world were forced to retreat. 14 years after the impact, technology finally caught up, and strongholds were built, protected by mighty walls sustained by a new energy source known as “bio-etheric energy”. The aptly named barrier cities became the last bastions of human civilization as the global government body known as the UNSC worked on a formal strategy with the intention of reclaiming the planet from the alien invaders.