The Second Great Schism lasted for a hundred years hence the nickname The Hundred Year Darkness. What happened was that a small group of knights began practicing extended uses of the force. These knights relied more upon the force leading them to see that the force could bend life its self. It could revive dead worlds, end death, and create new species. With their new powers these knights experimented upon other life forms creating new species as extensions of their will. Other Jedi watched these new force powers with suspicion, believing that such power could lead only to abuse. The earliest rebels from the first great schism known as the legions of lettow were defeated during the first war. However their legacy remained and inspired a new war. A new group of dissidents followed the same path. Many great Jedi such as Ajunta Pall, XoXaan, and Karness Muur. These dissidents tried to convince all the other jedi that they should join them. However the other jedi were careful and wanted to distance them selves from these rogue knights. The rogue knights believing their way as right the arguments turned into conflicts and The Second Great Schism began. The rogue jedi were then exiled along with their teachings.
Retreating from Jedi worlds such as tython the exiled Jedi raised an army of animalistic dark side abominations. The first forms of so called Korriban Zombies were created during the earliest part of the war. However even against these incarnations of the dark side the jedi began to push the exiled jedi back. The animalistic army was easily overwhelmed by the power of the jedi, but the exiled jedi refused to surrender. Duels to the death between jedi became the end of many battles. By the second half of the war, the exiled jedi were in despair. They were simply out numbered and had no way of winning. This is were one of the most terrifying acts of Dark side Alchemy took place. A creature of unspeakable horror was created. Its name the Leviathan, the dark jedi armies were reinvigorated due to this fearsome creation of the darkside. The Leviathans abilitys shocked both its creators and the Jedi Order. Instead of giving life it took it away. It fed upon it drawed upon it and it drained the energy out of its opponents completely. Armies fled in terror due to this creation and its ability to suck life. The way it was able to suck life out of anouther life form is unknown. However under the combined efforts of the jedi. The Dark Jedi were eventually pushed back and officially banned from known space. It is unknown what happened to the Leviathan. The Dark Jedi Wandered the Galaxy and eventually found the dark side planet Korriban.