Well, here's the timeline as requested. It will be available in a "posh" variant when the site goes live, but for now, if you like reading backround lore and walls of text, here is the "plain" version. If you spot inconsistencies or errors, feel free to comment! If not, simply skip, the ships will explode whether you know about their history or not! 
Great Pangalactic War Timeline
The war lasted for 10 000 years, and is thus divided into epochs. The reference date used by historians to set up a timeframe is the Formative Year, or simply Year 0, marking the date when Hegemony was formed between the Legion Alliance, the Consuls and what would later become known as the Multitude, some twenty million independent worlds or colonies belonging to various "minor" spacefaring races. Dates ranging prior to the Formative Year are marked as BFY, while those coming after the Year 0 are marked as AFY.
I. Epoch of the Schism (20,000BFY - 11,000BFY)
Called so because of the multitude of small brushfire wars which instigated a massive population migration inwards from the "southern" portion of the galactic perimeter, towards the largely unexplored regions of the galactic core and beyond, to the Nothern Rim. This migration mostly consisted of the destitute, the desperate and the despised from all corners of the galactic society. The most notable of these migrations is the Great Northern Drive, attempted by some hundred billion beings belonging to twenty different races inhabiting one of the star clusters most heavily impacted by the brushfire wars. These twenty migratory ofshoots will later become known as the Legion Alliance.
II. Epoch of the Pioneers (11,000BFY - 8,000BFY)
With the old powers in the Southern Galactic Perimeter slowly settling down after the long period of hostilities, and with the migrants already on the move for several thousand years, a new period of starkly differing societies is about to begin. While the old entities, exhausted and weary from their drawn-out wars turned inwards and thus initiated, more often than not, long periods of cultural and technological isolation which in some cases even led to a complete regression from their spacefaring status, the migrants are on the verge of cultural revolution. Emboldened by the vast, empty expanses of the galactic core, it is said that a thousand new colonies are founded each year. Resources are bountiful and so is space, and the emerging solar nations have no need to conflict with their neighbours over either.
III. Epoch of the Wall (8,000BFY - 6,000BFY)
Some eight thousand years before the birth of the Hegemony, the newly formed and densely intertwined nations of the galactic core decree the formation of a new superpower - the Legion Alliance. Consisting of the former outcasts and refugees from their old homelands in the Southern Perimeter, but now boasting economic and technological strength far superior to that of their old nations, the Legion Alliance will continue to dominate the nuances of the galactic society for two millenia. However, while at the same time seen as the shining example to all, they are also viewed with deep mistrust by several remaining major powers in the Southern Perimeter. This will lead to rising tensions over the next couple of thousand years, finally resulting in the erection of the "Wall", a string of key solar systems (some hundred thousand of them) spanning the southern circumference of the galactic core and acting as a sort of "border line" in the FTL avenues connecting the core with the galactic perimeter. The Wall is primarily used as a measure of quelling the paranoid Southerner fears of galactic domination by the vibrant Alliance.
None the less, the Legion Alliance continues to prosper, fueled by the abundancy of the resource-rich Core, while the Southern regions continue to decline, some colonies already reduced to their pre-spaceflight state and completely unaware of the greater galactic society.
IV. Epoch of the Great Smelting (6,000BFY - 5,000BFY)
A hitherto unknown race, calling themselves the Consuls, appears unexpectedly (and via unknown means) in several regions of the Southern Perimeter. They boast very advanced technology but are not willing to share or trade their secrets, prompting the customarily suspicious Southern nations to, once again, view the outsiders with mistrust. However, the Consuls are not interested in quelling any such fears either; on the contrary, on galactic date of 75.02.5785BFY, several massive Consul fleets begin to systematically eradicate all major remaining powers in the Southern Perimeter. Their purge seems to be limited to major centres of power only; independent colonies, regressed worlds or spacefaring races too weak to contribute significantly to any sort of resistance are left largely alone. The Southern powers, hopelessly outmatched by the arrivals' superior technology and faced with utter and swift destruction turn to the Legion Alliance only to find the Consuls already present in the Core, this time in the role of advisors and welcome as such, rather than conquerors. Whether through shrewd politics of the Consuls or due to simple resentment of the role the Southern nations had in their historic exile, the Legion Alliance refuses to get involved in what would later become known as the Great Smelting and watches their old masters be swept away, the remains herded and reorganized under Consul rule. The Multitude is born.
IV. Epoch of the Darklands (5,000BFY - 4,000BFY)
Following the reformation of the Southern Perimeter, the Consuls open the Wall to allow free flow of goods, people and information between the core and the South. Relations between the Legion Alliance and the South finally begin to steadily improve. However, not all is well. The expansion thrust which has guaranteed peace and prosperity within the Alliance is suddenly and startingly halted. Following several thousand years worth of expansion into the Northern Perimeter, the pioneer fleets have suddenly started to suffer losses and inexplicable dissapearances. While this was not unknown to happen throughout the Great Northern Drive, there were always survivors, or at least wreckage to indicate what peril had befallen the unfortunate settler fleets. This time, however, nothing is ever found. Thus the expanse of stars beyond the northern rim of the galactic core is quickly dubbed by the public as "Darklands" and by the 4,275BFY the Great Northern Drive gradually grinds to a halt.
V. Epoch of the Mustering (4,000BFY - 3,750BFY)
Deeply troubled by its inability to continue spreading into the Norther Perimeter, and suspecting an unknown but deadly foe lurking in the Darklands, the Alliance turns its awesome industry machine to war for the first time in its history. Great solar forges start churning out warships by the thousands every day and these brand new fleets are quickly crewed by the billions of frustrated would-be settlers eager to claim new territories for themselves, even at the cost of war with whatever is responsible for the dissapeearance of the initial unarmed settler fleets. Within a span of a couple hundred years, the Legion Alliance is able to construct the largest war force known in galactic history, dwarfing even the Consul fleets which so easily did away with the entire Southern Bloc.
The Consuls, however, remain unperturbed by this new development and continue their efforts of "re-integration" of the Multitude into a new, stable and compact, entity.
VI. Epoch of the Grasping Dark (3,750BFY - 2,500BFY)
The year 3,750BFY, when the Legion Alliance made its first armed push into the Darklands is now universally recognised as the opening year of the Great Pangalactic War. While there are plentiful materials available on the subject of the Legion Alliance's ensuing rear-guard action which would last for the next thousand years, very little is known about the beginning years of the War. Of some thirty million vessels sent to claim the Darklands, only an estimated ten percent ever returned to report, and even those reports were hazy at best. However, the lurking darkness which claimed so many lives so far is finally given a name - at the suggestion of the Consuls - "Xin", meaning "Outsiders" in the secret language of the enigmatic rulers of the South (it is ironic that even today, with the Consuls leading the Hegemony efforts to thwart Xin conquest of the galaxy, "Xin" remains one of very few words of their language known to the rest of the galactic society).
The Xin prove to be just as enigmatic, if not more, as the Consuls. All attempts at communication are flatly rejected, and virtually every encounter with them ends up in violence. That they seem to posess technological finesse on par with that of the Consuls does not help either. Throughout the Grasping Dark Epoch, The Legion Alliance's valiant efforts on recapturing the initiative melt before the Xin onslaught like snowflakes in a firestorm, as do their ships. Even though it enjoyed vast numerical superiority over the Xin for the most of the period, its inability to even slow down Xin encroachment of Alliance territory speaks volumes about the technological discrepancy between the two powers.
VII. Epoch of the Stand (2,500BFY - Year 0)
With the Legion Alliance losing badly, they turn to the Consuls for help in their struggle against the Xin. However, the Consuls refrain from sending their war fleets in aid of the Alliance, arguing that the time is not right for an offensive action and that the Alliance should instead cut its losses and retreat their still vast fleets behind the now long unused Wall, joining the Multitude and the Consuls and thus bolstering the Sothern Perimeter beyond any hope of conquest by the Xin.
The Alliance, somewhat predictably, refuses the Consul proposal, instead choosing to once more attempt a major offensive push against the Xin in an effort to drive them out of the galactic core and back into the northern expanse of the Darklands. By year 1,542BFY the entirety of the Alliance is reduced to less than half of its original territory before the outbreak of the War. However, the incredible resource wealth of the core enables the remaining star forge systems to achieve the impossible and, perhaps in a most heroic effort ever attempted by any star-faring nation, pour almost the very heart and soul of the Alliance into the greatest multitude of ships seen before or ever since. Sadly, biological lifeforms are not as easily and quickly constructed as machines, and it is said that at the end, even the young of the Alliance races were trained to operate its war-vessels.
However, it was not to be. As with the initial Great Fleet, the last stand of the Alliance was to prove their doom. Crushed by the overwhelming superiority of Xin war machine, now fueled by the vast resources of the northern core, the last Great Fleet of Alliance was fated to leave its metal bones scattered in the brilliantly lit skies of what was clearly no longer their home. The final losses suffered by the Aliance were devastating. Only ten percent of their total population managed to survive. Out of the founding twenty races, only three escaped total extinction: the Xergiz, the Ovalaar and the Myum. Out of the three, the Xergiz were the most numerous, perhaps because of their warlike nature and greatest tendency to shrug off hardships in the name of survival. The loss of so many lives and cultures left a deep scar upon their surviving brethren. THe loss for the galactic society as a whole may never be fully grasped. The present may have been starkly different today if it were not for the death of Varish and their collective quantum reality project. Music may never be the same without the gentle Lakra and their star-singer barges. And the loss of the great Library worlds of Bryn surely can never be compensated for. The damage was too great to ever be accounted for.
VIII. Epoch of the Hegemony (Year 0 - 6,245AFY)
Also known as the Standoff Era or the Epoch of the Bulwark, the period of some six thousand years since the formation of the Hegemony between the remnants of the Legion Alliance, the Multitude and the Consuls is largely uneventful when compared to the tumultuous ages prior. Under the competent Consul guidance, the newly formed hegemony quickly asserted its control over the great defensive structure spanning the width and thickness of the galactic disc, the Wall. Renamed the Bulwark Line, this section of space was quickly refurbished into the largest defensive formation in the galaxy, effectivelly cutting off the South from the Xin-infested core. Although the aggressive aliens did try to push through the Bulwark Line, the combination of the Consul fleets, their technological versatility, the numerical support of the Multitude and last but not least, white-hot rage of the defeated Alliance (now calling themselves Clans Remnant and refusing to take up permanent settlement as long as their old homes in the core remain occupied), proved too strong to be crushed so easily.
The Legion Alliance, reforged as the Remnant and bolstered by their industrial and technological aid from the rest of the Hegemony, now mostly consists of the Nomad Fleet; arguably the last Great Fleet of the old Alliance and while not a match in the sheer numerical grandeur of its precursors, much more dangerous for the scientific improvements provided by the Consuls. In accordance with the collective oath of the Clans Remnant after their defeat at the core, the Nomad Fleet constantly roams the Bulwark Line, guarding against frequent Xin forays at perceived weak spots, continuing their ten-thousand years long war against an equally unrelenting foe.
