The War of Power, also known as The War of the Shadow.
In the supposedly utopian society of the Age of Legends, Aes Sedai were frequently devoted to academic and scientific endeavors. However, the society of the time had advanced to the point that females and males each being able to draw strictly from a single half of the One Power had become an impediment to further progress. Then, a new source of energy that men and women could evidently both wield in equal measure was discovered outside of the Pattern. In order to gain access to this power, a team of Aes Sedai researchers led by the esteemed scientist Beidomon used the One Power to drill a hole through the Pattern and into the barrier that separated this energy source from the rest of reality. As it turned out, the source of the energy that the researchers had been attempting to access was the "True Power"; the essence of the Dark One. In creating the hole, they inadvertently breached the Dark One's prison and allowed his influence to begin spreading throughout the world.
The only immediate effect of the Bore being drilled was the spectacular destruction of the Sharom portion of the Collam Daane university. The more terrible, more subtle effects began to take root over the next hundred or so years as the Dark One's influence began to grow.
Where there had previously been a peaceful society, relatively free of major crimes, degenerate practices began to spread, violent sports became popular, and society began to decline rapidly. This period is said to have lasted anywhere from eighty to one hundred years. Not long after, the first people began to declare for the Dark One publicly and the first assaults were made against the established order of human civilization, originally with human armies, but then increasingly with constructs.
Since no records from before the Breaking have yet been found, virtually all contemporary knowledge of the age is based on documents written during the first few centuries after the Breaking. Numerous oral traditions have been passed down, but their accuracy is suspect and must therefore be considered "legends." The Aiel have the most authentic source of information about the age in the form of a ter'angreal in Rhuidean that allows Aiel hoping to be clan chiefs and Wise Ones to peer into the lives of their ancestors, including those living during the Age of Legends. However, these visions are scattered, random, and without context, making their use for historical record keeping somewhat dubious.
The overall timeline of the War is debatable. Events in The Shadow Rising indicate that the War lasted about three generations; perhaps around 50-75 years of fighting before the Breaking began. However, Robert Jordan has stated in the book The World of Robert Jordan's The Wheel of Time that the war lasted only about ten years or so. It is possible that the war was fought in earnest during those last ten years, while the violence of the preceding few decades merely involved the last, most savage stages of society's degeneration.
The War of Power
The War of Power began when enough people had declared themselves for the Shadow to amass armies. These armies, primarily composed of humans, began an assault on the decaying utopian civilization that the rest of humanity comprised. At this time, the concept of war was unfamiliar to those among humanity who had not been corrupted, so the forces of the Dark initially achieved quick gains before a war of attrition began. Aes Sedai, due to their ability to wield the One Power and as important academic and civic figures, frequently became the leaders of the forces of the Light.
At first the Shadow advanced rapidly against an unprepared populace, taking vast swathes of territory and a large number of cities. To make matters worse, a number of prominent and exceptionally powerful Aes Sedai began to defect to the Shadow for various reasons, becoming the "Chosen" or, as humanity dubbed them, the "Forsaken". The very first of these defectors was Mierin Eronaile, one of the researchers who first drilled the Bore. She declared her allegiance to the Shadow in the Hall of Servants itself, and rechristened herself as Lanfear. A number of these Aes Sedai, particularly Demandred, Be'lal and Sammael, were extremely adept tacticians and one, Aginor, was a geneticist/alchemist of extraordinary talent. It was he who was primarily responsible for engineering horrific human/animal hybrid constructs, the Shadowspawn, for use as the backbone of the Shadow's armies. These abominations included Trollocs, Myrddraal, Draghkar, Jumara, as well as more specialized constructs like the gholam. When each of these individual Forsaken defected is not known for certain, though it is known that Lanfear, Ishamael, Graendal, and Semirhage were amongst the first, and that Sammael was known to have defected relatively late in the war. The most prominent and powerful amongst them was Ishamael, formerly the highly esteemed philosopher and theologian Elan Morin Tedronai. At some point during the war, he was given the title of Chief Captain-General of the Shadow, making him the Supreme Commander of the forces of the Dark One.
Eventually, the Forces of the Light managed to sufficiently organize and began their first counter-stroke. The governing body of the Aes Sedai at the time, the Hall of Servants, took control of the Light's war effort and human society as a whole. Lews Therin Telamon, the highest ranking, most powerful, and most esteemed member of the Hall was, at least ostensibly, placed in overall command of the Light's armies. They pushed the Dark One's forces back heavily, retaking most of what had been initially lost. But during that time they discovered the terrible atrocities the armies of the Shadow had committed both when taking the cities, and later under the administration of the Dark One's followers. Cities retaken were little more than blackened wastelands, where people refusing to swear for the Dark One had been burnt alive at the corners. Retaking these cities became grim, horrific experiences which ultimately ended up consuming significant resources as the forces of the Light attempted to make these cities habitable again. With the drain on the Light's resources, the Shadow's armies, augmented by ever increasing numbers of Shadowspawn, again took the offensive and gradually began to push back the Forces of the Light as betrayals, low morale, and the Shadow's ability to manufacture soldiers wore humanity down. Additionally, the forces of the Light had to contend with a number of organizations that wished to sue for peace with the Forsaken. While a few of these groups looked at first to perhaps be succeeding, it was later discovered that virtually every single one of these organizations had been aiding the Shadow in some way, often unwittingly.
Eventually, the Forces of the Light began to succumb, due in no small part to the fact that the Shadow was willing to murder much of the population of conquered territories while the Light had to continue feeding and supplying their own civilization. Their resources thinning, the Forces of the Light could no longer sustain a protracted war, and were moving rapidly towards defeat.
However, according to Rand al'Thor after acquiring the memories of his past self, perhaps the primary reason for the Light's poor performance in the later stages of the war was the fact that there seemed to be little in the way of a formal chain of command for their armies. Though Lews Therin was at some point in the war appointed officially as the Supreme Commander of the Light's forces, so many amongst the commanders believed themselves above their compatriots that Rand described the situation as akin to having "an army of generals". He indicated that this caused a great deal of disorder amongst the Light's forces, and considerably blunted the effectiveness of the Light's military efforts.
It soon became clear to those fighting against the Dark One that the war needed to be won quickly if there was to be victory at all. However, the Hall of Servants was deadlocked on what to do. Two possible plans were espoused. One concerned the use of two great sa'angreal, one female and one male, to annihilate the Shadowspan armies and construct a second prison around the Bore itself, allowing the Dark One the run of Shayol Ghul but little else. These sa'angreal were, in theory, so powerful that either one could draw enough of the Power to destroy the entire world. Since no living human could stand to channel that much Power, "access key" ter'angreal would be required to shield the wielder from harm. However, some members of the Hall opposed this plan, citing that creating such weapons, or trusting anyone to wield that much Power, was too dangerous. Additionally, they pointed out that the Bore had expanded since it had been drilled, and that implementing this plan would simply allow the Dark One to continue chiseling away at his prison until he burst free, at which point they believed that no force at humanity's disposal would be able to contain him.
The other, proposed by Lews Therin himself, was to take a circle of the most powerful Aes Sedai to Shayol Ghul and re-seal the Dark One's prison. This plan was considered highly dangerous — Lews Therin himself admitted that there was little chance any of them would return, even if they succeeded. Furthermore, if the seals were improperly placed, attempting to re-seal the prison had the potential to completely rip it open instead. As it seemed that the plan to use the sa'angreal had fewer risks, a female Aes Sedai named Latra Posae Decume vocally and publicly opposed Lews Therin's plan, and made a pact with all the female Aes Sedai strong enough to be considered for use in Lews Therin's raiding party not to aid him. This "Fateful Concord," as it was later called, essentially nixed Lews Therin's existing plans, as the circle that he believed would be needed could not be formed without the cooperation of women. As such, the plan to use the Choedan Kal was approved by the Hall. However, Decume's public and vocal opposition to Lews Therin, and particularly the fact that the Concord's membership was composed entirely of female Aes Sedai, began to polarize both the Hall and the Aes Sedai as an organization along male/female lines.
Work on the sa'angreal surged ahead, but as the access keys were completed, armies under the command of Sammael overran the region where they had been undergoing construction. Fortunately, knowledge of the Keys had been contained to the highest level of the Light's military command, and Sammael never discovered their existence. With the Keys lost, Lews Therin argued again for his plan, reiterating his belief that using the brute power of the Choedan Kal would do nothing to actually contain the Dark One. He acknowledged the risks his plan was laden with, but believed it to be the only option humanity had left. However, Decume maintained her opposition, and the number of women pledged to the Concord had grown even to include women who were nowhere near powerful enough to take part in the proposed mission. This caused the polarization of the Aes Sedai to spread to unprecedented levels. Eventually, the Hall approved of a number of plans to retrieve the keys, but none of them succeeded.
As the debate continued, armies led by Demandred and Bel'al initiated massive offensive operations against the forces of the Light, which were barely contained. To make matters worse, Sammael began conducting a renewed offensive from his newly conquered territory. As the fighting from both these fronts threatened to overrun the areas with the actual Choedan Kal sa'angreal, it was speculated that the Shadow had discovered the existence of these new weapons and had begun a massive push to take them. These offensives and heavy fighting elsewhere, combined with wide-scale riots and demands by the Light's population to make peace, stymied the Light's efforts even further. It became clear to Lews Therin that, if any of the three offensives begun by the Forsaken managed to break through the Light's lines, the final defeat would be only months away. In light of Decume's continued opposition and the continued failure of the efforts to retrieve the access Keys, Lews Therin decided that he needed to take matters into his own hands.
Due to the gender-based polarization of the Hall, a small group of powerful young male Aes Sedai had emerged over the course of the war to vocally support Lews Therin against Decume. Popularly called the "Hundred Companions" (though there were actually one hundred and thirteen of them by the war's end), Lews Therin called upon them to undertake the raid on Shayol Ghul without help from any female Aes Sedai, planning to circumvent the Hall completely. As the Supreme Commander of the Light, Lews Therin was able to gather an "honor guard" of around ten-thousand soldiers without the Hall becoming aware. With these forces, Lews Therin Traveled directly to Shayol Ghul and began his attempt to re-seal the Bore.
Details are sketchy, since every man of the ten thousand died, the sixty-eight male Aes Sedai that survived went mad instantly, while the rest of the Hundred were thought to have been killed. What is known for certain is that, despite having no female aid, the re-sealing appeared to have been accomplished perfectly; the seals were all placed properly, the prison's overall integrity had remained intact, and the Dark One was once again rendered unable to touch the Pattern. To sweeten the victory, the thirteen most powerful of the Forsaken had been at Shayol Ghul for unknown reasons when the Bore was sealed, trapping them in Shayol Ghul and depriving the Shadow of it's most powerful warriors and most capable tacticians in one fell stroke.
However, all was not as it seemed, for sealing the prison had had a number of terrible consequences. In re-sealing the Dark One's prison, Lews Therin and his Companions had evidently needed to touch saidin directly to the Dark One. This touch allowed the Dark One to place a taint on saidin, driving Lews Therin and his remaining sixty-eight Companions completely insane on the spot. All of them immediately began a rampage across the world, destroying and killing indiscriminately. This madness drove Lews Therin in particular to murder his entire family and everyone else at his estate, and then to commit suicide when he realized what he had done. Additionally, the seal was apparently not as strong as the original prison itself had been, as saidin alone had been used to patch the Bore, which was but one aspect of two aspects of the Power that had been used to originally construct it. Though it was not known at the time, the seals would eventually weaken, threatening to allow the Dark One access to the Pattern again and freeing the Forsaken who were trapped there. Finally, the most powerful of the Forsaken, Ishamael, had somehow been only partially sealed behind the patch, and would emerge once every thousand or so years to destabilize civilization.
However, other than Lews Therin and his companions going mad, the effects of this couter-stroke were not immediately seen. To most, it appeared as though the Dark One's prison had been sealed, and the Shadow's leadership decapitated. The remaining Shadowspawn armies and the lesser Dreadlords were engaged by the armies of the Light, which included Decume, who evidently performed deeds of such greatness as to earn the title of Shadar Nor, which translated into later tongues as "Cutter of the Shadow" or "Slicer of the Shadow". Though the armies of the Shadow were routed, the true extent of the Dark One's counter-stroke soon began to manifest as the taint began to drive all male Aes Sedai insane. Some succumbed quickly, others took years, but inevitably, the taint drove each of them as mad as Lews Therin and his Companions. The only uniform aspect of this madness appeared to be an unprecedented desire/compulsion to destroy and kill with the Power. Entitled the Breaking of the World, this disaster was prolonged for many decades, and caused such devastation that civilization essentially ceased to exist until all the male Aes Sedai had died. It also caused destruction on such a cataclysmic scale that the surface of the world was irrevocably altered. Seismic activity in particular appeared to have been the underlying cause of the worst of the destruction. How and why the destruction was so widespread and thorough, or why the insane male Aes Sedai appeared to have been so unstoppable despite the existence of many female Aes Sedai, is unknown.
During and after the war, a number of Aes Sedai had a series of Fortellings which were compiled into the Karaethon Cycle. Apparently, before the Breaking, it had been realized that the patch on the Bore was imperfect, and that the Dark One would someday destroy it. The prophesies of the Karaethon Cycle were recognized as being a set of guidelines for the next incarnation of the Dragon, and every effort was made to preserve some form of them. Ultimately this endeavor was successful, as numerous copies of the prophecies survived into the Third Age, and their existence was common knowledge. Additionally, a number of other plans to aid the Dragon Reborn were put into motion at this time, such as the creation of the Eye of the World. Most importantly perhaps was the creation of Callandor, which the prophesies indicated would be the Dragon's weapon against the Dark One. To safeguard it, it was placed in the Stone of Tear behind such powerful wards that even the Forsaken could not hope to breach them. Additionally, a number of Power-related artifacts, Angreal, Ter'angreal, and two Choedan Kal access keys were taken by the Da'shain Aiel to a place that would eventually become the city of Rhuidean. Many of these artifacts would be of pivotal importance to the Dragon upon his rebirth.