While we were able to find solid and legitimate supporting evidence for essentially the whole story as it is written, it comes from a variety of sources and each of those pieces of information were likely written by a number of different people. This article strives to be more than a simple compendium of disparate lore tidbits. We took in all of the various bits of lore information and documented them in a chronological and readable way to produce the most complete story possible.
The developers confirmed in Devstream 52 that Warframe and Dark Sector is canon. As parts of what we do not know of the lore for Warframe can be explained by the Dark Sector story, this article includes some information and references to it and how it relates to Warframe lore. However, Steve Sinclair noted that Dark Sector is not a direct prequel to Warframe. As of now, DE has confirmed that Warframe and Dark Sector are inextricably linked, but not a canon prequel, though a lot of WARFRAME's ideas were inspired by their original rendition of Dark Sector.
This page will be regularly updated as the developers, Digital Extremes, release more information.
The Story/History of Warframe
Orokin Era
Long before current events, the Origin System was run by a race called the Orokin. It appears that the Orokin were the dominant humanoid faction at the time. For a time, the Orokin ruled the Origin System and spent a great deal of time building large outposts and experimenting on genetic samples of creatures found on Earth. The Orokin created a race of synthetic beings, which later are known as the Sentient, to spearhead an expansion of Orokin influence beyond the Origin System into the Tau System.
Old War
From this point, the Old War erupted between the Orokin and the Sentient (Presumably from the Tau System that the orokin were attempting to expand into). With their ability to subvert high levels of technology, the Sentient quickly overwhelmed the Orokin. The Orokin quickly discovered that their method of fighting proved ineffective against the faction.
Faced with losing the war, the Orokin intended to create something that could replicate and fight in an autonomous way like the original proto-sentients did. It is possible that this weapon was the Infestation, and that this was likely unleashed on a part of the general population to create vast amounts of troops. However, the Infestation soon spread out of control and assumed a mind of its own. The Infestation itself appears to have had little effect in slowing down the advancement of the Sentients and merely served as a means to make gates, ships, or orokin weapons useless to the sentients who could not adapt to the mutations.
The Orokin, now desperate, sought to exploit Void energy after an accident aboard a spacecraft called the Zariman Ten-Zero led to a number of children developing Void powers and abilities. They took full control of the Transference program that was mean to heal the children, and instead rushed the project into weaponization. The Warframes were a parallel technology, and a synergy was found where the Tenno could use Warframes as conduits for void energies and utilise their newly developed abilities as a lethal asset. Excalibur was possibly the first Warframe created during this time.
The tenno were often forced to link with these frames by less than gradual means, which often resulted in Warframes going berserk and/or the tenno going temporarily insane with pain and confusion, which is described in the Rhino Prime codex entry.
After the process of Transference was more or less perfected, where the Void energy was focused and controlled for specific tasks, the Tenno-guided Warframes are revealed to be very efficient killing machines and they actually manage to push back the Sentient to the brink of defeat. The Orokin managed to recapture the Outer Terminus, and quelled the threats of the Origin System. The Sentient however, were not defeated without launching their last agent: Natah.
The Collapse
Natah was a last-ditch Sentient who had been created with the sole purpose to take control over the Tenno themselves. She infiltrated the Origin System, but was not able to prevent the Orokin forces from recapturing and crippling / destroying the Outer Terminus. The Orokin were victorious at the time, but the Tenno chose to betray the Orokin – ultimately triggering a history point known as The Collapse (alluded in the Stalker's codex).
The war was over, the Sentient now gone and the Orokin now destroyed, all Natah had to do to was finish her mission to annihilate the Tenno. However, due to what is revealed as a "gap" – a state where a part of a Sentient become corrupted when crossing over to the Origin System, she was unable to execute this mission and instead grew a humane affection towards the Tenno themselves. She ended up betraying her last mission and took the Tenno as her own children, becoming known as the Lotus.
The Grineer, who were workers and/or slaves to the Orokin, took advantage of the choas to spring revolts all across the system, stealing orokin ships and weapons while also securing the cloning technologies that created them, alluded to in the Guardsman codex entry. During this period, the two Orokin Twins used this opportunity to enact revenge, and began to amass armies of loyal Grineer to their cause which eventually lead to them becoming the sole rulers of them.
It is unknown of the exact origins of the pre-Corpus, whether they were lowly orokin servants or worshiping colonists of some description, they eventually made a grasp on the system shortly after the Grineer rose to power, quickly occupying wrecks and crash sights on various planets, to scavenge the technology and grow. Eventually, the two powers grew equally in power, and began to trade technology to the Grineer in exchange for raw materials or currency.
Warframe Era
Some indeterminate number of centuries later, the Corpus are widely considered the governing force in economics and research. The Grineer both fight with the Corpus for power and buy technology from them to support their constantly degrading bodies. At one time, the Infested had all but conquered a few of the Origin System's planets but have been pushed back to their residence on drifting ancient Orokin Derelicts and recently conquered Eris, apart from the occasional outbreak on populated planets. All that is left of the Orokin are the forgotten Prime weapons they either built or had a hand in building, and towers in a dangerous area known as the Void.
The Tenno are becoming reawakened by the Lotus, not remembering anything of their past. Many Tenno awake from Cryosleep already connected to a Warframe that the Lotus informs them how to use, unaware of their true nature. They are then set loose upon the solar system either alone or in small squads to tackle a wide variety of missions designated by the Lotus to maintain balance between the Grineer and Corpus factions or to quell Infested uprisings.
The Corpus also start to make an attempt at rebuilding the Outer Terminus. In the meantime, Grineer researcher Tyl Regor finds and breaks open the vault where an ancient Sentient was held within. Sentient Oculyst drones are sighted by Tenno across the Origin system. Other Sentients are said to be entombed in other locations. Signs of the Sentient are very clear, and it is hinted that they will return to the Origin System to reconquer what they have been defeated with.