Gameplay
Gameplay is initially focused on base and unit construction. The player starts with a single HQ building and a few basic units, usually just one building unit. Subsequent focus then shifts to capturing and holding strategic locations on the battlefield. These control points are captured by infantry squads and provide resources to construct additional units and buildings or unlock certain units in an army's tech tree. Battles are won either by holding a certain number of control points for a period of time or by destroying all of the opposing armies' HQ structures.
Resource management
Two primary resources exist: requisition and power. These resources are not harvested or otherwise gathered by the player's units. Instead, requisition is generated constantly by the army headquarters. The player can increase the rate at which requisition is acquired by using infantry squads to capture and control certain "strategic points" on the battlefield. These points can be reinforced with defensive structures that also increase the rate of requisition accumulation. Though resources are unlimited, all sources of requisition will eventually decay, dramatically decreasing their supply rate.
Power is gathered by building generators, with each headquarters supporting up to six generators. Additionally, some maps have "slag deposits", upon which more powerful generators can be constructed to produce power faster. As the player progresses up the tech tree, reliance on power increases.
In addition to these primary resources, the Orks also have Ork resource. Ork resource is generated continuously by Waaagh! banners and is used up when creating Ork troops and vehicles. The number of banners and the size of the Ork population determines the Ork's Waaagh! level which in turn determines the technology level the player has access to.
Warfare
Infantry units are given orders as squads rather than as individuals. Most fully reinforced squads consist of about 10 units. The squad moves and attacks as a single entity. Squads can produce and replace their own units anywhere in the field. They can be equipped with special weapons and have heroes or special units attached to them. For example, a Space Marine squad starts with 4 marines, but can be expanded up to 8 standard marines and a sergeant, and individual marines can be equipped with heavy weapons. The player is also free to choose particular upgrades and can specialize each squad for a specific purpose.
Vehicles are highly resistant to standard infantry rifles, so they must be targeted with specific weaponry (e.g. rockets) to be destroyed. Vehicles can also be upgraded with multiple weapon systems, usually differentiating between anti-infantry and anti-vehicle armaments.
In addition to a typical hit point system, infantry units also have morale. Morale applies to a squad as a whole. When morale drops to zero, the squad "breaks;" at this point the squad's accuracy at a range, damage dealt in mêlée, and defensive capability while using cover are significantly reduced, however the squads movement speed is slightly increased. The squad's morale will regenerate on its own while the squad is not in combat. Some weapon types, such as flamethrowers, are made specifically to demoralize the enemy. Favorable terrain gives units a defensive cover bonus, while water and swamps slow units down and decrease their defensive ability.
Setting
The game is set in the Warhammer 40,000 universe, a dystopian vision of the future with gothic undertones. Humanity has forged a galaxy-spanning empire, The Imperium, with the Immortal Emperor as humanity's leader and God. The Imperium is in a state of constant war with the Orks, Eldar, and the human servants of Chaos. The single player campaign is set on the planet Tartarus.
Factions
Warhammer 40,000: Dawn of War features four playable armies.
The Space Marines are the elite genetically modified superhuman soldiers of the Imperium. Space Marines have the highest morale in the game. Their troops and vehicles are more expensive, however. The Space Marines are the only playable race in the single player section of the game, and the 11-mission campaign features the Blood Ravens chapter as the protagonists, led by Captain Gabriel Angelos and Librarian Isador Akios.
The Chaos Marines are traitors that have chosen to abandon The Imperium and their duties to humanity, and instead worship the Gods of Chaos. In Dawn of War, they use troops that are similar to their Imperium counterparts. In addition, they employ morale-draining daemons and Psykers. The campaign features the Alpha Legion, with their leaders, Sindri Myr and Lord Bale.
The Eldar are an ancient, technologically advanced race. Eldar in Dawn of War are fast and fragile. They are able to move quickly across the map via webway gates. The campaign features the craftworld of Biel-Tan, and their leader, Farseer Macha.
The Orks are a savage, warlike race. In large enough numbers, they gain morale immunity. The tech tree for Orks differs from the other races in that it depends on the amount of orks currently in your army and the number of erected WAAAGH!! banners. Several clans are featured in the campaign, as is the Ork Warboss, Orkamungus.
In addition to the four fully playable races, the Imperial Guard also make appearances in the single player campaign as allies of the Space Marines, led by Colonel Brom. They would later be made into a featured race for the first expansion pack, Warhammer 40,000: Dawn of War: Winter Assault.
Plot
The Single player campaign is set on the planet Tartarus, an Imperial planet that is currently being besieged by a large Ork Waaagh!! The campaign begins with Colonel Brom and his 37th Tartarus Planetary Defense Force Regiment under attack by a large group of Orks. The Blood Ravens 3rd company, led by Captain Angelos makes planet fall and saves Brom and his remaining men and then proceed to exterminate the remaining Orks in the vicinity. In the aftermath of the battle, Gabriel is joined by the Librarian Isador Akios. Brom asks Isador about a recently conducted Exterminatus of the planet Cyrene, however Isador makes it clear he is not to bring it up again. The Blood Ravens then prepare for a mission of extermination of the Orks surrounding the port, in order to protect the evacuation craft.
Isador, sensing that the Captain's mind is troubled, realises why, and tells him that there was nothing he could have done to save his home planet of Cyrene. However, Gabriel tells him not to mention it again, stating that his homeworld was his responsibility. After the extermination of the Orks, scouts reveal to Gabriel that Chaos are operating on the planet. Soon after this they are joined by an Inquisitor, Toth, who orders them to leave the planet, warning that a Warp Storm is approaching the planet and will consume the planet in 3 days time. Toth orders a complete evacuation of the planet. On further investigation, it is revealed that the Eldar are also operating on the planet. The Blood Ravens find an altar dedicated to Chaos, confirming Gabriel's suspicions, and resolves to destroy the traitors, unknowing that Isador is already under the influence of Sindri, the Chaos Sorcerer of the Alpha Legion.
Upon destruction of most of the remaining Eldar by Gabriel's forces, the Farseer pleads with Gabriel to heed her words; however during their moment of distraction, Sindri steals an artifact, which Macha reveals to be a key to "the undoing of this world". Upon inquiry,the Farseer shows surprise at their ignorance, commenting that the Inquisitor 'keeps them on a short leash' and implying that he knows more than he is telling, and advises them to ask him, before telling the Blood Ravens where to find the entrenched Chaos forces. Gabriel and Isador confront Toth in the ruins of an Imperial Temple, following a pitched battle with Alpha Legion forces, who reveals that the world is cursed, and bears an artifact of chaos: the Maledictum, a stone that contains the essence of a daemon. The forces of Chaos now bear all that they need to unearth it. Toth also explains that the Eldar were fighting to protect the stone, as it was they who imprisoned the demon in the stone originally: as he puts it 'as Chaos's oldest enemy, the Eldar see themselves as the only capable defence against its influence. And we have paid for their arrogance'. Toth also says that the power of the Maledictum is enough 'to turn the faithful and drive men mad', having already corrupted much of the population of Tartarus and the Imperial Guard, as well as affecting the Blood Ravens somewhat. Gabriel and Toth form an alliance and make plans to find and destroy the Maledictum, however, Isador is then completely overcome by the temptations of Sindri and chaos, and resolves to steal the Maledictum for himself.
The Blood Ravens destroy the army of Lord Bale, who was betrayed by Sindri, during which time Isador seizes his chance and steals the Maledictum. In the face of Isador's betrayal, Gabriel pursues him in an effort to bring him to justice. The Blood Raven forces are successful in destroying Isador’s troops and Gabriel defeats Isador in single combat. Isador pleads for forgiveness to Gabriel. Gabriel tells him, "If redemption is what you seek, then redemption is what you shall get," before shooting him in the head with his bolt pistol, using him as an example to his men about the dangers of Chaos.
Meanwhile Sindri has used the power of the Maledictum to turn himself into a Daemon Prince. Inquisitor Toth bequeaths the Daemon Hammer God-Splitter to Gabriel. They then, with the Blood Ravens and the aid of the remaining Eldar forces of Farseer Macha, attack the Chaos forces, eventually killing the daemon prince Sindri. The final scene sees the Eldar and Blood Ravens standing around the Maledictum. Despite the warnings of Farseer Macha, who begs them not to destroy the stone, Gabriel obeys Inquisitor Toth and his own judgement, and destroys the Maledictum with God-Splitter. The Eldar forces then retreat, Macha warning prophetically Gabriel has doomed them all, and the Blood Ravens leave to be evacuated. However, Gabriel stays back, and encounters the Daemon of Khorne which he unwittingly released from the Maledictum. The daemon lets Gabriel and his men leave safely as thanks for its release, but tells Gabriel that he will soon come to claim him and his men. Gabriel vows to destroy the daemon, before following after his departing men.