Nosgoth's Temporal Logic
Parallel Timelines: Parallel or "forked" versions of history do not exist in Nosgoth - only the current iteration of history is considered "real". If a historical paradox occurs and a timeline is derailed, the derailed timeline is considered to be "dead", and can never be revisited. Timelines do not split or actively co-exist, and a new one can only be spawned if the current one is subject to a paradox and derailed.
Observed Timelines: Nosgoth's history was altered three times throughout the Legacy of Kain games. As such, four timelines have been observed in the series, two or more being explored in both Blood Omen: Legacy of Kain and Soul Reaver 2. They are not formally named in official sources, and can only be identified by the order in which they came to exist.
First Timeline: Most of Blood Omen: Legacy of Kain takes place in the first timeline. Towards the end of the story, at the very instant where Kain kills William the Just in the stronghold of William the Just, the assassination of William the Just occurs, killing this timeline and spawning a new one.
Second Timeline: The concluding events of Blood Omen: Legacy of Kain, the entirety of the Legacy of Kain: Soul Reaver comic and Legacy of Kain: Soul Reaver, and the early stages of Soul Reaver 2 take place in the second timeline. During Soul Reaver 2, when Raziel defies history by refusing to kill Kain in the Sarafan Stronghold, this timeline is derailed by the sparing of Kain by Raziel and dies, making way for a third.
Third Timeline: The latter events of Soul Reaver 2 are portrayed through the third timeline. When Kain saves Raziel from entering the Reaver in the Sarafan Stronghold, he triggers the sparing of Raziel by Kain, spawning another new version of history.
Fourth Timeline: The conclusion of Soul Reaver 2, as well as the entirety of Blood Omen 2, the Legacy of Kain: Defiance comic and Legacy of Kain: Defiance, occur in the fourth timeline. This version of history has not observably been subject to a paradox, and remains the current "living" timeline of the Legacy of Kain series.
Continuity Between the Timelines
From the games alone, it is not possible to determine the full extent of the changes incurred by each paradox (and, hence, the exact nature of the differences between each timeline). However, some facts can be ascertained:
The raising and corruption of the Pillars, the formation of the Circle of Nine, the forging of the Reaver and the slaughter of the Circle occurred in all four timelines.
The Battle of the Last Stand and the Legions of the Nemesis were only present in the first timeline. When the Nemesis was prematurely killed by Kain in the assassination of William the Just, these elements were removed from history and ceased to exist.
Moebius's mercenary army, its renewed vampire purge, and the execution of Vorador (which left Kain the only remaining vampire in Nosgoth) was a product of the assassination of William the Just. These elements did not exist in the first timeline.
The events of Blood Omen 2 (and Legacy of Kain: Defiance) were "made possible" by Janos Audron's resurrection in the fourth timeline at Raziel's hands. This did not occur in previous timelines, and therefore these events could not have unfolded in the same way.
The events of the Soul Reaver era were not changed or affected in the third or fourth timelines. Even after paradoxes, they still unfolded as depicted in Legacy of Kain: Soul Reaver.
Soul Reaver 2 establishes that history admits only the slightest alterations to the timeline possible, so it can probably be assumed that many events and elements between the four timelines witnessed are consistent between the paradoxes, even though only limited information is available to confirm the full extent of this persistence in canon. The fourth timeline is the most comprehensive and coherent version of the history of Nosgoth, prospectively including events witnessed in all of the Legacy of Kain games and media.
Historical Timeline
"Historical Timeline" is a Crystal Dynamics text outlining the chronology of the Legacy of Kain story. Crystal Dynamics created at least three official versions of "Historical Timeline", covering the events of Blood Omen: Legacy of Kain, Legacy of Kain: Soul Reaver, Soul Reaver 2, and Blood Omen 2:
"A Brief History of Nosgoth" was included in "Legacy of Kain: Funk Soul Brother", an article in issue 36 of Official U.S. PlayStation Magazine in September 2000.
"Historical Timeline", a condensed version, was included in Soul Reaver 2's bonus materials.
"Chronological Events (as conveyed in BO:LoK and SR)", the most comprehensive version, was an internal Crystal Dynamics document. Series art director Daniel Cabuco kindly released this document to the Legacy of Kain Wiki team for archival.
The Legacy of Kain Wiki team also presents an unofficial version with additional detail, covering the events of the Legacy of Kain: Soul Reaver comic, Legacy of Kain: Defiance, and the Legacy of Kain: Defiance comic.
Events of Blood Omen: Legacy of Kain
Altered Historical Timeline:
Kain returns to present-day Nosgoth and discovers that assassinating William 50 years ago triggered a renewed vampire purge.
Vorador is executed; Kain is the only surviving vampire in Nosgoth.
Kain confronts and kills Moebius, the Guardian of Time.
Kain confronts Mortanius, the final Guardian, at the Pillars - Mortanius is destroyed as the Dark Entity possessing his body emerges; Kain defeats the Dark Entity in combat.
With Mortanius' death, all but the Balance Pillar are restored.
Kain realizes finally that he is the Balance Guardian, and therefore the last of the Nine.
He must choose between sacrificing himself to heal the world... or preserving his life and ruling Nosgoth in its damnation.
Kain refuses the sacrifice, ensuring the Pillars' collapse.