- Main article: Terrans
Humans have long waged war with each other. This has not changed when interstellar travel was discovered. The game is vague on the events between now and the beginning of the campaign; however, a war called the 'Succession Wars' is mentioned to have occurred just before the Tau Ceti incident in the briefing of the very first mission in the Terran campaign. After the war, humanity is more or less united, and the Terran Navy is as strong as ever.
Harsh realities of war have forced Terrans to create powerful warships to defend themselves. Since energy shields are a fairly recent addition to ship defences, most ships are forced to rely on their great hull strength to keep them intact. This, in turn, forces humanity to constantly expand in search of resources necessary for ship construction. The Navy is made up primarily of capital ships with Corvettes making up the bulk of the fleet. The most powerful ship class in the Terran Navy is the Dreadnought with powerful cannons and a shield that can be overloaded to make the ship invulnerable to damage, though this ability chews into the ship's supplies, and will soon have to be returned to a friendly repair/resupply platform or HQ. The Terrans also possess powerful battle-stations called Ion Cannons, capable of destroying most ships with one shot from half of a system away. An Ion Cannon's main drawbacks are its slow turning speed, low rate of fire, and high supply use, forcing them to be placed inside a friendly resupply ring if the player doesn't want a resupply ship to be stationed next to it at all times. Terran units and structures cost proportionately more Ore resource than any other race in the game, but their larger ships also require an almost equal amount of the Gas resource, as well as the Crew resource. Again, the larger/more advanced the ship or platform, the more resources needed to construct it.
- Main article: Mantis
"Mantis" was the name given to the first alien race discovered by humanity because they have much resemblance to the Praying Mantis on Earth. The Mantis are insectoid, more than twice the height of humans, and have a hive-like social structure, ruled by a queen. Unlike Earth insects, the entire Mantis race has only one queen, and the first-born female offspring of the queen is the sole heir to the throne, often causing sibling rivalry. An example of this sibling rivalry is when the Mantis Warlord Ker'Tak rebels against the Mantis empire, and enlists the help of humanity to destroy the queen, Warlord Ver'Lak. Because of their high reproduction rate, the Mantis are constantly searching for new worlds to colonize and, if necessary, conquer. They tend to see all other races as inferior. It is also very consistent in Mantis behaviour to sacrifice many for a higher purpose, as stated by Celareon Magistrate Elan in the briefing of the 12th mission in the Terran campaign.
Driven by their need for more worlds, the Mantis have created powerful fleets to further that goal. Because of their hive-like mindset, the majority of the ships tend to be carriers, sending swarms of fighters to overwhelm the enemy defences and crush them without putting the main fleet itself in jeopardy. This same mindset explains why the strongest Mantis ship is the Tiamat Super-Carrier, which can launch multiple wings of heavy bombers to leave the enemy no chance of escape. If all fighters/bombers are destroyed, however, the carriers are left completely defenceless. That is why they are also supported by other close-range Mantis craft. Mantis units and structures cost proportionately more of the Crew resource than any other race, similar to how Terrans use more of the Ore resource and how the Celareons use more of the Gas resource.
- Main article: Celareon
Very little is known about the origins of this race of pure energy. Cursed to spend their lives trapped in mechanical containers, they nevertheless praise their unknown creators. Celareons possess extremely advanced technology. They are even able to create artificial wormholes, and this knowledge is coveted by the Mantis and is one of the reasons the two races are in conflict. Celareons consider themselves to be peaceful and are only interested in the pursuit of knowledge. They do, however, realize that they live in a hostile universe and must, therefore, protect themselves. While usually Celareons are unified, there have been disagreements regarding the war with the Mantis: some believe that peace should be made at any cost, including handing over the artificial wormhole technology to the Mantis; others claim that the Mantis cannot be allowed to get their hands on the technology, as it could allow the enemy to bypass the static wormhole network and strike at the very heart of Celareon space.
Like Terrans, Celareons prefer capital ships to fighters. Unlike Terrans, they have no fighter capability. To a human eye, Celareon ships look like giant creatures of the sea. Their graceful, nearly transparent looks hide deadly weapons and defences, which they do not hesitate to use when threatened. The most awe-inspiring ship - the Monolith, ensures that most enemy ships do not survive an encounter with the Celareon fleet. Because the Celareons are by nature a peaceful race, most of their ships (Except the Trireme and Monolith, the two most powerful Celareon ships in the game) are not well-suited for close-combat, instead possessing better range and supply. Furthermore, the Celareons possess very powerful and diverse static defensive weapons structures. Celareon units and structures cost proportionately more of the Gas resource than any other race.
- Main article: Vyrium
Originally, Conquest: Frontier Wars was supposed to have four races but this was changed before the game was released. There are still traces of the fourth race's code in the original game. The lizard-based Vyrium were then announced to become available in the sequel, Conquest: Vyrium Uprising, which was unfortunately cancelled as well.
The Vyrium were, however, supposed to be a mutated, warrior race that were somehow imprisoned by the Celareons. It's suggested that they escaped from Celareon clutches, and eventually became a full faction of beings that live and fight for their own survival. From the Vyrium Uprising Demo, we know that the Vyrium have their own super-weapons, including the means to destroy planets. This is another reason for their escape, to evade persecution from those who believe planets shouldn't be blown apart at will.