However, during the confrontation with the Warboss, the shuttle which ferries Sindri and Bale away is spotted by a Blood Ravens' scout. Unknown to the Space Marines, however, the Orks' invasion was in fact engineered by the Chaos Alpha Legion's Sorcerer, Sindri Myr, as a smokescreen to their operations on Tartarus, using the forces of Sindri's supposed commander, Lord Bale. These include key tasks such as the elimination of their leaders (including an Ork Warboss) to destabilize the Orks' fighting spirit. The Blood Ravens' Space Marines, upon descent to the planet's surface, secure Tartarus' spaceport and start their own operations against the warring Orkish forces. The story of this campaign also sets the stage for the events of Dawn of War II - Retribution. The single player campaign is set on the planet Tartarus, an Imperial colony under siege by Ork invaders, with the player taking the role of the Space Marines' Blood Ravens 3rd Company, led by Captain Gabriel Angelos, that arrives to assist the planet's 37th Tartarus Planetary Defence Force Regiment of the Imperial Guard, led by Colonel Carus Brom.

The Imperium, desperately fighting to preserve the human race from extinction, is in a state of constant war with alien species like the Orks or Eldar, as well as insurrections from renegade worlds or the human servants of Chaos, who employ demonic forces and sorcery under either of the Chaos Gods they serve, having deliberately betrayed their once godlike Emperor of Man. The game is set in the Warhammer 40,000 universe: a dystopian vision of the far future in which humanity has forged a galaxy-spanning empire, The Imperium of Man.

Warhammer dawn of war 3 steam download