You've got the order mixed up. Golden Age: The age in which Humanity spread through the Stars thanks to the Traveler. Collapse: The Arrival of the Darkness and the war between it and the Traveler. Humanity wars with the proxy forces such as the Hive. This is when some humans are transformed into the Awoken and the Exos are crafted as additional support. The Collapse is so named because it signals the Collapse of the Human Empire. Everyone is forced back/retreats to Earth. Dark Age: Following the Collapse, everything is lost. Cities are no longer defensible. Orbital Defenses go silent. Manufacturing grinds to a halt. Forward progress on Science and Technology is lost and starts to go backwards. Communication networks are gone. Survival is not guaranteed. Work begins on the foundation of the Last City and rumors circulate of it's reputation as a safe haven. Ghosts are confirmed as existing. Toward the end of the Dark Age, the first Guardians come into being. City Age (Current Age): In the waning years of the Dark Age, Guardians go to war and establish themselves as defenders and protectors of the Last City by holding it's borders until defenses are emplaced to truly turn the Last City into the safe haven it's rumored to be. The City Age begins when the walls are completed and the Last City no longer suffers invasion. Guardians go forth into the wilderness to scavenge remains of the Golden Age to be reversed engineered. Survivors are found and brought allowing the pursuit of Science and Technology from what remains in their safe haven. Manufacturing begins again. Light and Hope return to those under the Traveler. A long time has passed since the Collaspe/Dark Age. To you it was only a single moment between your death and rebirth. To the rest of the world its been an eternity. You still died and when that happened, your brain suffers damage. Look at modern head/brain trauma victims. Spotty memory is sometimes a result of when brain tissue is damaged, ether by physical trauma or lack of blood circulating which starve and kill it. For Exos, the circuitry is a very dedicate thing. You drop your phone or computer enough you'll break connections and bits that require the circuits to function like memory causing things to corrupt and erase when they can't be read. Whether by blunt trauma or the erosion of time and the elements.