The Dark Age began with the Blackout (as opposed to the Jihad's whiteout) of 80% the HPG network on August 7th of 3132. Humanity was suddenly thrust back into the early days of space travel where FTL communication was not possible and messages had to be couriered by JumpShips. This made command and control of armed forces and the governing of the Inner Sphere empires very difficult, if not impossible. Just two years earlier, Devlin Stone, founder of the Republic of the Sphere, retired and vanished, promising that he will return when the Republic needs him the most.
The blackout allowed the Houses, Clans, and other powers both within and outside the Republic to begin reclaiming or conquering worlds they had ceded to or that had been taken by the Republic. Before long, military factions whose loyalty lay with one of the Great Houses or Clans began to organize and take action against the Republic government. Several Republic officials, planetary leaders and nobles, and industrial giants who pledged their allegiance to the greater powers of the Inner Sphere supported or, in some cases, headed these factions. House Liao was the first of the Great Houses to invade the Republic, claiming worlds like Liao, which the Confederation had grudgingly surrendered after the Republic used military force to claim the world. The other Houses quickly followed suit, using the gains of their factions to make footholds deep in the Republic.
Besieged from within and without, Exarch Jonah Levin, on October 1, 3135 enacted Fortress Republic. This plan created The Wall, a barrier which prevented jumpships from passing across it, keeping Republic forces "inside" and every one else "outside." This reduced the borders of the Republic to roughly the size of Prefecture X, leaving the loyal supporters of the Republic outside the Fortress to fend for themselves. As part of this action, no one can leave or enter the Fortress.
Also during these events, Jessica Marik (Halas), daughter of the false Thomas Marik, engineered the re-formation of the Free Worlds League. She also legitimized her claim to the House Marik legacy by marrying Thaddeus Marik, scion of the line of Alys Rousset-Marik. She largely succeeded in her re-formation plan and was pronounced Captain-General of the re-formed Free Worlds League on July 3, 3139.
Devlin Stone emerged from a cyrosleep he had been in since he disappeared. In 3149 Stone deactivated the Wall, allowing Republic forces to leave and other forces to enter Republic space. However, when Capellan Confederation and Clan Wolf JumpShips attempted to reach Terra, they learned that the Wall still remained, though now it only protected Terra. Clans Wolf and Jade Falcon began a full-scale invasion of the Republic of the Sphere.
The Dark Age is the setting for the Collectible Miniatures Game MechWarrior: Dark Age (and subsequently MechWarrior: Age of Destruction). The story is largely told in the 30 novels of the MechWarrior: Dark Age line:
- Ghost War, Michael A. Stackpole
- A Call to Arms, Loren L. Coleman
- Ruins of Power, Robert E. Vardeman
- A Silence in the Heavens, Martin Delrio
Book one of The Proving Grounds trilogy
- Truth and Shadows, Martin Delrio
Book two of The Proving Grounds trilogy
- Service for the Dead, Martin Delrio
Book three The Proving Grounds trilogy
- By Temptations and By War, Loren L. Coleman
- Fortress of Lies, J. Steven York
- Patriot's Stand, Mike Moscoe
- Flight of the Falcon, Victor Milán
- Blood of the Isle, Loren L. Coleman
- Hunters of the Deep, Randall N. Bills
- The Scorpion Jar, Jason M. Hardy
- Target of Opportunity, Blaine Lee Pardoe
- Sword of Sedition, Loren L. Coleman
- Daughter of the Dragon, Ilsa J. Bick
- Heretic's Faith, Randall N. Bills
- Fortress Republic, Loren L. Coleman
- Blood Avatar, Ilsa J. Bick
- Trial by Chaos, J. Steven York
- Principles of Desolation, Jason M. Hardy and Randall N. Bills
- Wolf Hunters, Kevin Killiany
- Surrender Your Dreams, Blaine Lee Pardoe
- Dragon Rising, Ilsa J. Bick
- Masters of War, Michael A. Stackpole
- A Rending of Falcons, Victor Milán
- Pandora's Gambit, Randall N. Bills
- Fire at Will, Blaine Lee Pardoe
- The Last Charge, Jason M. Hardy
- To Ride the Chimera, Kevin Killiany
- A Bonfire of Worlds, Steven Mohan Jr.