There is no question that the Blood War is the most significant event on the Planes; having gone on since the dawning days of sentience, this battle for the supremacy of Law or Chaos has marked not only the Lower Planes, but the whole of the multiverse for eons on end, seemingly never-ending in its bloodshed and violence. No one can walk the planes for long before encountering something, somewhere, or someone incontrovertibly touched by the Blood War, and hardly ever the better for it.
The Blood War is almost entirely a fight between the baatezu of Baator and the tanar'ri of the Abyss, a balance between the perfect obedience of the baatezu and the tremendous numbers of the tanar'ri; their first battles marked the beginning of the war, and every major event in its history has been at the hands of one or the other. Thousands upon thousands of each fiend are spawned to serve as nothing but cannon fodder for the gristmills that are the front lines of the Blood War. On the side of the baatezu, the Blood War is largely run by the Dark Eight, a collection of eight pit fiends dating back to the original fall. Once soldiers of Asmodeus himself, today they are charged with leading the forces of the baatezu in battle, arranging for materiel and intelligence support, handling diplomatic military arrangements with outside organizations, and any other related duties that may fall under the purview of the War. The tanar'ri of course have no such structure, but some Abyssal Lords have more direct interest in the Blood War than others. Pazuzu, Graz'zt, Alzrius, Lissa'aere, and Vucarik are amongst those known to have the greatest interest in the War, though it's rare the Lord with absolutely no stake in it whatsoever; somewhat surprisingly, though, and in contrast to Asmodeus, Demogorgon indeed does have little to no interest in the War, perhaps having gained his fill in service to the Queen of Chaos long ago. And while not all tanar'ri have spent time on the battlefields, those chosen for it must fight or face the wrath of the molydei, who are always hunting for deserters, or simply travelers that can be impressed into the Abyssal ranks. Of course, while these two fiendish kinds may comprise the majority of forces on the Blood War battlefields, there are more than a few others that involve themselves for their own varied reasons.
Chief among these are the yugoloth, the fiends of the Grey Waste. Mercenaries for hire by either side, they offer their talents in combat, infiltration, or tactical planning to the highest bidder, their long-practiced skills often turning the tide one way or the other. They seem to have no allegiance but their own, perfectly willing to serve which ever side suits them so long as the price is right. Not always something as simple as gold or gems, but arcane knowledge, prisoners, any one of a variety of opportunities that they find suitable for the task requested. Some even say that the Blood War persists by their hand, the slaughter guided towards one direction or another according to their hidden desires towards some unknown end; while the same has been said about nearly every planar event of any significance since the dawn of history, the far more blatant involvement in the Blood War leads many to wonder if in this situation it might not be true.
A surprise to some, the modrons are in fact a significant force in the Blood War as well, aiding the baatezu in demonstrating the ultimate supremacy of Law. Though not precisely allied with the baatezu per se, Primus has no desire to see chaos win out to any degree; as such, he has committed to the Blood War efforts the Army of the Blood War, a force nearly one million modrons strong, separate from the Mechanus military heirarchy. While this force does occasionally cooperate or coordinate with baatezu actions, far more commonly they are simply sent out against front-line tanar'ri strongholds or forces, fighting alongside baatezu but not entirely with them.
The celestials, however — contrary to the thoughts of many Primes — most commonly keep far away from the Blood War. There are some exceptions, the renown Sword of Vengeance being one of the most prominent such, but since both the betrayal of the eladrin by the tanar'ri during the Tanar'ri Rebellion (resulting in the Sorrow of Androlynne) and the utter failure of the Celestial Invasion to do any more than turn the full force of both fiendish armies against their might, the result of the Celestial Schism that followed was to leave the forces of Good hesitant to step in, for the large part relieved that the War at least keeps both fiendish kinds distracted from other matters that might have their attention otherwise. The end result of the Celestial Invasion was enough to bring even the highest of celestials the awareness of what a focused fiendish army could truly do without the Blood War to draw its ire. Rumors fly that there may even be sects amongst the celestial kinds that go so far as to encourage the Blood War through arms trade or information warfare, though such claims are solidly dismissed as ludicrous whenever brought before the celestials.
Though many may be tempted to, one cannot ignore the impact of the thousands and thousands of mortal mercenaries hired by both sides on the Blood War. While in terms of pure numbers these men and women are hardly noticeable against the backdrop of warfare, mortal contribution has long been marked as providing the most unexpected developments in the War since its earliest day, even into recent years. Further, the Blood War remains the top employer of mercenary force across the planes, and has since the first mortals stepped upon it, despite the immense mortality rates and the trauma such battles as are found in the War can inflict. This has had quite the impact on mercenary companies upon the planes, with nearly all having to account for it outright in one fashion or another: whether it be full-on devotion to one side or another, open hiring by either baatezu or tanar'ri if the pay is good, assignments on a person-by-person basis, or any number of such schemes. And of course, more than a few such companies have even taken hard lines against Blood War employment despite the lucrative contracts it brings, if only that they don't lose employees faster than they can acquire them.
Finally, there are minor contributions or involvement by nearly every other significant culture upon the planes. The slaadi, perhaps surprisingly, are rarely involved as they are just as likely to strike against tanar'ri as baatezu should the whim strike, their innate individuality ironically giving most of them no great devotion to chaos as a philosophy; as a result, the tanar'ri hesitantly call upon them thanks to this innate unreliability. The rilmani grow involved only when the balance seems to be tipping too far in one direction or another, but the Blood War is such a wide-ranging and embroiled conflict that even they at times have trouble seeing the balance held at any given time; thus, it's rare to see a rilmani even at a significant Blood War event. And the more minor planar peoples — the gehreleth, the bladelings, the githzerai and githyanki, etc. — while certainly fighting from time to time (often in either a general self-defense or a mercenary role), rarely have any consistent or notable devotion to the War.
Amongst the baatezu, initial preparation for a Blood War sortie occurs either from Avernus or from Stygia, depending on if the destination is to be reached by gate travel or via the River Styx; the former is far more common, as it relies less on the somewhat unpredictable winds and ways of the River, but depending on situation, the Styx may be judged a reasonable necessity. Once armed, supplied, and verified, squadrons are dispatched in strict regiment, with travel proceeding across the Great Ring if battle is to be met merely in Gehenna, but via the Outlands or, rarely, even through Sigil itself if a more distant destination.
Baatezu forces are divided into three units, known as "Commands". The most commonly encountered is the Third Command, led by generals Bel, Meritos, and Hanariel; this Command is the rank-and-file of the baatezu armies, with the majority of the ranks filled by the least of their number. Lemures and nupperibos make up the vast majority of most battles, herded into combat by the thousands, if not millions for the especially significant conflicts, most often shepherded by spinagon or abishai, or rarely a less-talented barbazu not deserving of higher duty, to ensure they stay on track. The higher ranks of most combat consists of the First Command, led by generals Alusiel, Phanior, and Galarond, made up of air forces and elite unites. The barbazu are most commonly seen in the thick of things, the most vicious of Baatorian soldiers, with abishai providing magical support, hamatula serving as advance scouts and patrols, and erinyes keeping the entire collection directed, passing along direction from above. The average First Command unit is led on the field by a handful of cornugon or gelugon, but in especially large battles, entire squadrons of these baatezu will be sent out, led by pit fiend generals on the battlefield. It's only these greatest of battles that bring forth pit fiends, most instead preferring to direct battle from afar via divination and telepathy, passing along orders and guidance to the cornugon who then filter it down as needed to the lower ranks. Finally, the Second Command is the naval command, under the leadership of generals Kobbis, Meathe, and Laginus. Though sea battles are rare in the Blood War, the Second Command is charged with transporting any units that require sea- or river-travel, including ferrying along the Styx; as a result, their support is key in many battles. The ranks of the Second Command are largely filled with abishai and erinyes, with lesser ranks not trusted to handle themselves on the Styx without losing their minds; osyluths make up the majority of lieutenants and boatsmen, with amnizu and, less commonly, cornugons filling the upper ranks.
In contrast, the tanar'ri have of course little order to their way of things. Nearly all tanar'ri embarkations are made from the realm of Durao, but this is simply due to its Stygian piers also holding convenient access to the Plain of Infinite Portals, allowing for both quick collection and quick dispatch of forces both willing and not; while it's strictly avoided in the case of the baatezu due to lack of time to learn their specific stratagems, the tanar'ri (specifically, the molydei) have no compunctions about conscripting any and every bit of aid they can find, whatever plane that may be. Tanar'ri armies are a morass of fiends and "allied" forces with no rhyme or reason, occasionally but not consistently armed and supplied by the master of a given battle. Once enough of these soldiers are gathered, they're sent out to fight as soon as possible (if only to avoid the in-fighting that inevitably occurs when too many tanar'ri are in the same place for too long), sent out by whatever method has been chosen by whoever happens to be leading this gathering of forces. At times speed is the desired factor, at others surprise, but contrary to common belief, there is at least some sense and thought put into tanar'ri battle plans; perhaps not nearly as much as the baatezu, but it is far from random happenstance and feel as they may claim.
The lowest ranks of the tanar'ri are filled by manes and rutterkin, directed by dretch infantry that do their best to keep these mad figures pointed at the proper enemies, and babau keeping them all on track. The barbazu are matched amongst the tanar'ri by the buleazu and armanites, both fearsome fighters in their own regard, the former prone to unbreakable bloodlust while the latter quite skilled at sudden hit-and-run force. Alu-fiends provide arcane support, while cambions either fight alongside the other ground forces or act as advance scouts and infiltrators, a dual role also filled depending on situation by bar-lgura and maurezhi respectively. Goristroi serve as living siege engines, similar in some respects to mortal army elephants, and often ridden in a similar manner into battle by entire squadrons of fighters more adept at ranged combat. Vrocks serve as the elite fighters, adept both at aerial combat and at acting in surprising concert to direct their innate and powerful magics against foes. A given sortie will most commonly be led by a marilith or balor tactician, with a collection of hezrou distributed throughout the ranks to relay orders and ensure that the demands of the leaders are born out; under threat of punishment if necessary, but the Blood War is of such deep importance to so many tanar'ri that such threats are rarely necessary, the lesser following these demands out of pure respect for the devotion and intelligence they show (yet quick to act independently if they see what seems a better option).
Once arriving at the battlefield, the least of both sides are the first sent into the fray, thousands of lemures and nupperibos sent directly into at least as many manes and rutterkin, each side quickly followed behind by their greater forces. While occasionally shock tactics and surprise strikes are done by both sides, thanks to natural telepathy, summoning, and teleportation any such strike rarely keeps advantage for long, as any surprised party can usually call upon support near-instantly. (Though there have been more than a few times where the defending party in a surprise attack was slain before they could call upon any of these resources.) Baatezu nearly always fight in rigid formations predetermined by their generals, quickly regrouping and rearranging in practiced patterns to respond to differing terrains, conditions, and situations, while tanar'ri more often than not charge in en masse, seeking to overwhelm both by force of numbers and by pressing until a weakness is found and pouncing.
Blood War battlefields are a mess of swinging blades and blasts of magical energy flying in all directions, a hazard not only to combatants but to anyone in the general area. And while fiends are resistant to many forms of magical energy, let alone their innate resistance to magic in general, this by no means reduces their usage on the battlefield. Far too useful a weapon to simply abandon because it isn't guaranteed, the many-varied innate magical abilities and learned spellwork of fiends are let fly in all respects, even if only to strike out against equipment or non-fiendish aid. In fact, because they possess so much innate, theoretically-inexhaustible magic, battles between fiends tend to involve even more prolonged magical use than any mortal fight. The average mortal magic duel rarely lasts beyond three minutes, but a Blood War strike can easily stretch on for an hour before one side is devastated or destroyed, innate magic striking out all the while. This of course has significant impact on local conditions, and with so much magical energy released over such a relatively short period of time, strange effects often follow in the wake of a Blood War battlefield; wild or dead magic zones, tears in space, necromantic hot zones, and spellhaunts are amongst the more common, but the specific results depend on the precise conditions, which can rarely be predicted in advance.
Of course, the innate magic that poses the most significant difference to fiendish warefare is their natural innate teleporation. Thanks to this ability, possessed by the higher ranks of both forces, as well as the disconnected nature of Blood War battlefields, there is little sense of "side" to such combats, and following the initial contact there is no sense of front or rear rank in a given battle, nor any safety gained by any one position in a given battlefield relative to any other. This is not to say that fiends are constantly blinking about every second, but it does mean that tracking the events of a given battle can be extraordinarily difficult even in the best of situations. Despite their natural teleportation, though, Blood War battlesites tend still to be quite concentrated, for two reasons. For one, just because you can blink away as well as your foe doesn't mean you automatically know where exactly they blinked to, and thus a retreat away from the battlefield tends to be successful. (Not to mention effects like the natural unpredictable teleportation of Oinos, for example.) Second, however, is that Blood War battles are often fought not over arbitrary tracts of land that just happen to be contiguous as in mortal wars, but over land, artifacts, or even people of some sort of value to one side or the other, and as such battles tend not to stray much from that target or else they may as well simply be giving it away to their opponents.
The Blood War, as is known to many sages, has as its origins a much older, yet much more protracted war: the War Between Law and Chaos. This conflict was fought in the ancient past between the then-ruling kind of the Abyss, the obyrith, and the Wind Dukes of Aaqa, with the archomentals offering aid to both sides as their outlooks saw fit. The obyriths, led by the Queen of Chaos, fought against the elemental forces of Law via their servitor kind, the tanar'ri; one of the first efforts at transmuting the spiritual entities that filled the planes into new, plane-appropriate forms. This war came to a head in a region known as Pesh upon the world of Oerth, in the ancient prehistory of that place. (In fact, the only reason the battle has been associated to that world is mention of the nearby iconic White Plume Mountain and recent extraordinarily-ancient tombs found in their vicinity.) The forces of the Queen of Chaos were defeated via the Rod of Law, a creation of the Wind Dukes of immense power, that enabled the imprisonment of then-Prince of Demons Miska the Wolf-Spider deep within the depths of Pandemonium. The Rod, however, was shattered in the battle, transforming it into the artifact known today as the Rod of Seven Parts. The resulting loss was so great that the Queen of Chaos pulled all forces from the war, and without her help, the Archomentals of Chaos fell to simple infighting against the Archomentals of Law. However, the Wind Dukes themselves were utterly decimated; though they did indeed defeat the Queen of Chaos, only but a handful remained to celebrate it.
With this weakening of their obyrith masters, the tanar'ri saw their chance. Calling the aid of the eladrin for ending a slavery that had lasted millennia, they together overthrew the obyriths, executing or exiling as many as they could grab. And once their revolution was complete and their grip on the Abyss was unquestionable, they turned on the eladrin, slaughtering them and driving them out from the plane. Thus the tanar'ri stood as masters of the infinite depths, the few surviving obyriths nothing but a relic of days gone by.
Meanwhile, across the Lower Planes in Baator, the baatezu had little interest or even awareness of the events of the War. Their focus in these early days was entirely upon the Prime Material Plane, as per what was both then and now seen as one of the highest duties of the baatezu: the corruption of mortal souls. They were not blind to the planes — in fact, there had always been the occasional skirmish between baatezu and tanar'ri since their first chance encounter upon the Grey Waste some time hence, though nothing so fervent as today — but it simply paled below their chief duty. It was in fact not until that great battle upon the Fields of Pesh that Asmodeus and his lessers first bothered to turn their attention to this matter. To them, this great victory in the name of Law seemed to say it all. Though the Wind Dukes may have largely passed on in their victory, its implication still held true in their eyes: Law was supreme over Chaos. And so they may have continued, self-satisfied in the proof of their own superiority.
But then the tanar'ri didn't fall, and for the first time, and perhaps the last, Asmodeus was surprised. They in fact improved their position in the fall of the obyriths, contrary to all he could have expected. They flaunted the very essence of Law with their success in the fate of their own defeat, a contradiction that could not be solved. And so the skirmishes grew and grew in intensity, the baatezu wishing to demonstrate to the tanar'ri what they ought to have learned after the defeat at Pesh, and the tanar'ri wishing to bow to no power in the name of utter freedom through force of arms. While there is no one specific fight that can be said to be the start of conflict, the Blood War had begun.
The earliest times in the Blood War were in many ways the most successful for both sides. It was mere years before both forces noticed how force of belief could literally move entire regions under the domain of one or another side, and the battles for the weakest portions of the Lower Planes were intense to a degree that had never before been seen. It was common in these days for total warfare to erupt in Avernus or Pazunia themselves, even on occasion deeper layers of each plane. And occasionally these battles were even successful at hauling a portion of Baator into the Abyss, or a piece of the Abyss into Baator, not to mention the effects on Carceri, Gehenna, or the Grey Waste itself. So much was in flux in the first centuries of the War that one could not even truly define a front line to the fighting.
Over time, though, these triumphant victories slowed amongst both sides, with each growing more accustomed to the tactics of the other, starting a mutual arms race between the two to find any weaknesses that could be exploited in the other. Neither could stray far from their own inner nature, of course, which made any significant amount of study hopeless. Still, there were the occasional shining examples of new stratagems, spellworks, or devices emerging from this rush to outsmart the other. The great Four-Cross of General Bel, the strategem that cemented his reputation for tactical genius and placed him at the head of the Third Command, emerged from this time period, as did the tanar'ri Mask of the Pit, though it was significantly less successful. In fact, many spells still used today are said to have come about from this very research, only to filter down through the millennia, having lost all fiendish connotations in the intervening time. Lesser spells of summoning, circles of protection, dimensional locks and anchors, all and more are believed to have come from the Blood War.
As the Blood War gained in force and presence, it began to worry the celestials. The archons and angels had already had much to unnerve them in the baatezu, many of whom (especially in those old days) had not so long ago stood upon the Mount with them. The eladrin had much to hate about the tanar'ri after their betrayal. And now this War which seemed to threaten to embroil the entire multiverse if left unchecked. They could not stand for this, and they knew that while these fiends were distracted with their war, the celestial host could move upon them and cow the fiends with the full force of their arms. Millions upon millions of celestials moved upon the Lower Planes as a single great unit, looking to end the danger once and for all.
Little could have diverted the fiends from the Blood War even at this early time, but the mass invasion of millions of celestials was certainly it. And they hadn't counted on a key fact: these were people that had spent centuries warring, that had learned techniques, methods, weapons, and magicks that the celestials hadn't even dreamed of. Though the fiends never truly worked as one, they put aside their differences in the short term in repelling the invading armies, a postponement of their battle until this threat could be dealt with. It was a year-long slaughter for the celestials; of all the millions that went into the battle, only a few thousand survived to the end of the year to return home. The loss was so devastating and such a blow to morale that it sent the survivors and their home superiors into a philosophical tailspin leading to a general policy of withdrawal from direct combat and action only to protect innocents.
The Powers Intercede
Following the failed invasion, centuries upon centuries passed of continuing warfare, before even the powers themselves decided to try and bring an end to the fighting and bring forth victory in their name once and for all. While most of the Lawful powers were hesitant to intercede due to questionable clauses in the Pact Primeval, and the more significant Chaotic powers cared little for planar affairs, especially in these early days before planar travel had come to their mortal followers, some minor powers of the Abyss felt that were they to gain favor with the tanar'ri and help lead them to victory, it would surely lead them to greatness of their own. They may have sought to make a blow against the forces of Law, to spread chaos by whatever means, or perhaps even the worship of the tanar'ri; whatever the individual reasons, the first alliance between tanar'ri and power was thus forged, an agreement between the fiends and Thuon, an intermediate single-sphere power of chaos and destruction that called the Abyss home. And once that first agreement was made, other powers soon fell in alongside the tanar'ri in Thuon's wake: among others, Laogzed, Loki, Kanchelsis, and Ekwensu all offered their aid against the baatezu.
It must be pointed out that today the idea of a power directly fighting alongside mortals, even upon the planes, in a matter not directly involving another deity is ludicrous. In these early days, however, the planes were seen by most powers as purely under their purview, and the Divine Compact held little in the way of restrictions on deities acting against other planar beings. And so indeed, the deities physically manifested upon Blood War battlefields, nearly always to great success. Of course, this divine involvement drew attention from others, and while even the minor Lawful deities did not wish to embroil themselves into the minutiae of the Pact Primeval, they did not wish the War to end so abruptly and so destructively, the violence already wreaking havoc even beyond Baator. Thus a number of deities of Law interceded, if only to combat the deities of Chaos walking the battlefield. Then followed more deities of Chaos, more of Law, and so on until it almost seemed that was once a battle purely of the fiends may have turned to an all out battle of the very powers themselves.
But then, an act that none could have predicted: the utter death of Thuon, not at the hands of another deity, but at the hands of the baatezu. None are sure how it was accomplished, but all present watched him wither to nothing before the eyes of those in combat, his avatar shriveling to dust at the same moment that his corpse manifested upon the Astral. The baatezu were quick to claim the credit, and none stepped forward to contest it. This act, whatever means were applied to bring it about, struck true terror in the hearts of the collected deities for the first time they could remember. The idea that fiends, beings barely a step above mortals, could bring about such an act without divine aid was enough for the gods to immediately withdraw all direct involvement, limiting themselves, as on the Prime, to the aid of followers alone. And much as with the celestial invasion, this act defined general policy for deities for ages to come, with the following Godmoot occupied almost wholly with discussion on proper reaction to the death of Thuon alongside the task of appending the Divine Compact to include restrictions on planar manifestations, if only for the mutual safety of the divine.
Some deities still involve themselves in the Blood War today, of course. Many powers of war in all its varied form, from Kiri-Jolith to Morrigan, send their followers in to fight, enjoying the rush of the vastest war in existence if vicariously, while others encourage it more indirectly, supporting it much as the rumored celestials simply so the fiends do not cease their efforts and turn their attentions outwards; St. Cuthbert is such a power, for example, as is Arvoreen. However, they each are wary not to grow too involved, that they do not themselves face the lesson poor Thuon endured so long ago.
And So It Goes
With the failure of the powers to truly join directly, the Blood War was able to role on largely unchanged for millennia upon millenia. Both sides grew increasingly staid, with battles far too evenly matched for either to make any significant progress. Morale ticked away bit by bit, plummeting upon the spread of the Illithid Empire as the flow of petitioners to both the Abyss and Baator slowed to a trickle, souls that may otherwise have been destined for or seduced to their lands instead pulled into the hopelessness of the Grey Waste, brought to Carceri thanks to the betrayal of their peers to the illithid, or even lost to the planes entirely thanks to a complete loss of belief. For nearly a year, the War halted but for the rare skirmish as both sides regrouped, seeking means of dealing with this lack of petitioners; it was during this time that the larva trade with the Waste first came into vogue, the night hags of Hades first finding their calling as soul traders if only to supply the forces of both sides.
Indeed, morale was such an issue during this time, an entire settlement of lesser baatezu rebelled thanks to encouragement by the tanar'ri, rising up against their superiors and spilling entirely over to chaos in a successful repeat of the much older Mask of the Pit gambit. While the rebellion was quashed by Dark Eight themselves (following the decimation of a squadron of balors that hoped to take advantage of the situation by the rebels themselves), this still sent a message deep into the heart of the Lords of the Nine: things could not be allowed to continue as they were. They recognized that something must be done to bolster their numbers, and began seeding the Prime with various rituals and magicks, means of calling upon the baatezu that would allow them more influence than the conjurers might hope. The tanar'ri were quick to follow suit, of course, and soon mortals themselves found ways of modifying the rituals, some (but not all) removing the hidden flaws and loopholes left by the baatezu. Thus the first binding spells began to spread through the Prime, as well as possibly the first rituals of possession, and even perhaps the first reproducible recipe of lichdom. This increased planar contact with the Prime further led to the first major incursions in the opposite direction, mortal mages reverse-engineering the spells of summoning to develop the first spells of planar travel, making first inroads onto the planes and becoming the ancestors of the first planars; largely reptilian in this era, as reptilian societies were far less likely to be taken by the illithid. And while the Illithid Empire faded within the millennium of the Rebellion, it marked the first sign that where the planes may have failed to turn the course of the Blood War, perhaps mortals in sufficient means or ways could succeed where they failed.
In the centuries and millennia following the fall of the Empire, a surge in fiendish callings to the Prime began, and unsurprisingly, the first waves of half-fiends, cambions, alu-fiends, and tieflings followed soon after. And through them, a new rush of creativity was brought to the Blood War, the flexibility of mortals bringing new perspectives that the rigid beliefs of the baatezu, and even the tanar'ri, had never thought of. Not bound by the strictures of a specific framework of philosophy or morality, the new blood thought in ways their ancestors never would have, though at times tainted by thoughts of mercy, justice, or other such concepts also beyond fiendish mindsets. Not merely half-fiends, though, but the first significant wave of liveborn fiends also came about during this period, if bringing with it many of the same stereotypes associated to mortal-blood. The second wave of fiendish exploration was soon to follow, each side picking up on the adventurous spirit of mortals and seeking out lost relics or places of power that could turn the tide in the War; this second Age of Exploration was most marked by the first discovery of Sigil by the tanar'ri, kicking off a number of failed attempts by both tanar'ri and baatezu at taking the city.
The Chasm Erupts
With new blood, new resources, and the flow of petitioners from the Prime restored to its former levels if not greater, the Blood War surged for the next millennia, on occasion spilling over to the Outlands, the Astral, Acheron, Pandemonium, and even for one brief occasion Sigil. This period of the War was marked, as mentioned, by wholly new developments: new breeds of fiends, new weapons techniques, the first experimentations at ritualistic replacement of innate fiendish powers, and even applications of spellwork taken from mortals, including the introduction of construct and undead soldiers to the ranks. This surge could not last forever, of course, and eventually it settled down as new habits engrained themselves and new lines were drawn. The increasing planar presence of mortals, however, led to even more sources of bodies for combat, with the introduction of the first mercenary companies to the planes a welcome sight to the generals of both sides.
Eventually, as complacency wore in, and even some of the oldest fiends sought an end to the violence, there erupted a great yawning chasm upon the Grey Waste directly beneath the yugoloth Fortress Ghoresh. This great pit, known afterwards as the Ghoresh Chasm, shows striations both physical and auratic along its length indicative of both the shifting tones of chaos and the rigid lines of law, intertwined in a spiral formation along its length down as far as any could observe. Exploratory yugoloth parties sent into those depths were lost, and analysis by oracles, sages, and diviners of the patterns along its surface suggested that only a perfect cooperation of law, chaos, and neutrality could unlock whatever secrets it held.
And so for the first time in thousands upon thousands of years, the Blood War halted, this time a full truce called between the baatezu and tanar'ri with yugoloth mediation that they might cooperate and investigate this pit and determine just what the Ghoresh Chasm meant and what it implied. For months, the two forces sent their best minds to analyze the chasm, with all observers watching with bated breath for the other shoe to drop. A conclave of the three sides was established about the Chasm, and the highest ranks for once agreed to meet in person to discuss matters. Generals Bel and Ilssender, amongst the most decorated of the baatezu and tanar'ri respectively, were to lead the meeting with any number of lesser squadron leaders and diplomats.
Unsurprisingly, however, the conclave quickly fell to blows, upon something as minor as General Ilssender refusing to move from General Bel's assigned seat. The entire force of baatezu and tanar'ri struck at one another, with any number falling into the chasm's depths, as the yugoloths for once utterly failed to bring about any measure of control over events. Both sides retreated from the chasm but for a smattering of fiendish sages that had hid themselves from the combat, and the Blood War once more erupted in full force. Though erstwhile attempts at resuming the truce on behalf of returning to study the Chasm began here and there, never again have they reached any measure of success, to the great frustration of the yugoloth as well as those few sages still willing to cooperate if only allowed to do so.
Following the failure of the truce of Ghoresh, the Blood War returned much as it had been, though Prime contact began to grow into even greater prominence. In this time some of the most significant Prime civilizations of the so-called Modern Era were at their peaks, including many still well-known today: Netheril, the Suel Imperium, and the Thri'Kreen and Al'Malamut Empires being among the most written-on. With them and their arcane experimentations came a new wave of mortal exploration and a vast increase in summonings, deals, and planar contact in general. Though the invigoration brought about by new blood wasn't nearly as all-encompassing as it was previously, it did bring with it new mercenary blood not nearly as weary, as well as a heightened sense of morale on both fronts that their efforts may be showing some success by bringing new mortals to their causes.
Over the centuries, these new mortals settled throughout the planes, forming new planar populations, while the Blood War pressed on. As always, little to no progress was achieved by either side, the two forces evenly matched. Then, in a surprise to all, a significant blow was struck: the death of XXXXXX, self-proclaimed lord of the undead, not by any baatezu force but rather by the demigoddess Kiaransalee; such a thorough attempt at purging him from existence that his very name was removed from every record throughout all reality. One of the three most significant Abyssal Lords in the entire plane, his armies of undead were considered a key backbone to Blood War efforts, and with his death these armies were lost in but an instant, either de-animated or released of their own accord. The tanar'ri scrambled to make up ground, unsure whether to seek some means of restoring XXXXXX or to call upon Kiaransalee's offer to replace the forces; by then, Lolth had herself held some significant forces in play in the Blood War, and few were eager to risk her ill will in such a dark time. Other planar forces were simply not an option, far too risky to make up such slack. Yes, surely the tanar'ri numbers could make up the difference eventually, but losses were already beginning.
They found aid, however, in an unexpected ally. The Dustmen, themselves transient allies of XXXXXX, offered their own fairly considerable necromantic services in his name. Here was an organization with no prior bounds to the Blood War, and with fairly considerable resources, that had slipped entirely under the glance of the tanar'ri. And so their eyes were first opened to the factions of Sigil and the potential they held. Indeed accepting the aid of the Dustmen, they began seeking contact with the other factions that seemed to hold common purpose with them. Within mere years, the baatezu followed suit, Bel in particular quick to solidify connections. The Sign of One and Mercykillers aiding the baatezu, the Revolutionary League and Fated aiding the tanar'ri, and the Doomguard offering their knowledge to both. Bringing far greater strength and ambition to both sides, sending the Blood War surging further out into the planes than it had been recorded in ages, at times even touching upon the Upper-side regions of the Outlands. And so the War as it is today stands, far more intertwined with mortals than it ever had been.
While today the majority of fighting occurs on Carceri, Gehenna, and Grey Waste, it's hard to determine any specific front lines due to the fluctuating nature both of planar travel and of the armies themselves. Still, it is rare that any significant combat happens outside these three planes, or even outside Othrys, Khalas, and Oinos.
As of Hashkar 127, the tanar'ri look to be gaining ground on the baatezu, thanks in large part to the recently completed ships of chaos constructed by a joint tanar'ri/Doomguard venture. These massive vessels, while not unstoppable, have proven quite near to such in most every baatezu encounter yet recorded. This advantage is sure not to last long, of course, as none does, but it does mark a possible new direction for the War to come, the institution of constructs and artifice not merely for arms or soldiers, but true war engines in the fiendish arsenals. Recent rumor has it that the War may reach a new pitch in recent days, perhaps brought about by the pure existence of these massive weapons of war; there's word spreading of baatezu seeking aid for their own battles in the most unlikely of places: the Beastlands. While appearances of the baatezu in the Beastlands have increased sharply in recent months, many are eager to see what precisely this rash of sightings bodes for the War.
- Fiendish Codex I: Hordes of the Abyss, pg.106
- Guide to the Astral Plane, pgs.44,77
- Hellbound: The Blood War
- In the Abyss
- On Hallowed Ground, pg.42
- Planes of Chaos: Book of Chaos, pgs.14,19,21,26
- Planes of Chaos: Mosntrous Supplement, pg.2
- Planes of Law: Baator, pg.12
- Planes of Neutrality: Adventures in Chaos, pg.24-32
- Planes of Neutrality: Liber Malevolentiae, pgs.36,46
- Planewalker's Handbook, pg.116