Setting: Earth's future
21st Century: A spherical object the size of a small moon arrived on Mars. It would come to be called the Traveler and a manned mission - Ares One - was sent to investigate its intentions. The Traveler used its power to terraform planets in the Sol system, allowing life to flourish in locations that would otherwise be uninhabitable.
Golden Age: The period following the Traveler's arrival. Centuries of prosperity and technological advancement. Humanity's lifespan tripled and they spread to planets and moons outside of Earth.
The Collapse: The Darkness' arrival in the Sol system, bringing about the end of known civilization. Humanity fell back to Earth and was all but wiped out. The Traveler's last act during this time was to create the Ghosts.
Dark Age: Post-Collapse, what remained of humanity wandered the Earth in search of the Traveler while the system was set upon by aliens. During this time, Ghosts began to find and resurrect certain souls as Guardians, wielders of the Light.
City Age: Humanity converged beneath the dormant Traveler to form a city. Over time, walls were raised and it became a haven for the remnants of humanity.
Six Fronts: A legendary battle in which the Guardians fought off an alien attack.
Twilight Gap: An enemy race known as the Fallen combined forces to launch an assault on the City. The Guardians held them off at Twilight Gap - a pass in the nearby mountains.
The Great Disaster: The Guardians attempted to reclaim the Moon but failed with hundreds of casualties.
The Reef Wars: A series of conflicts between the Awoken and the Fallen House of Wolves.