The Sons of Darkness, the first known major Land of Mountains government, was founded by a band of shinobi mercenaries, a scientifically advanced shinobi clan that used their knowledge to conquer and enslave other clans throughout the Land of Mountains. The Sons of Darkness rose to new heights when, approximately two years before the First Great Ninja War, they successfully combined the power of chakra with genetic technology, creating wondrous effects that seemed, to them, to border on the mystical. Due to this achievement, they used their technology to explore the land. However, when they found clans less advanced than themselves, they conquered and enslaved them rather than benevolently aid their advancement. The Sons of Darkness, officially established in at the start of the First Shinobi War, dominated pockets of the land for almost ten years and enslaved numerous developing shinobi clans including the Amejouten, Tsurugi, Gurasu, and the Yama. At its height, it consisted of more than 500 enslaved-subject villages with a population of ten thousand sons (the name of any official mercenary in the group) and one million slaves.
The chakra-based technology of the Sons had profound consequences which led to the total collapse of the organization. The technology began feeding off its masters' aggressive tendencies and created dark chakras that further corrupted its creators. After generations of supremacy and control, the Sons of Darkness began to fracture. Huge slave revolts erupted throughout the borders of the land along with various factions vying for control. This led to a civil war throughout the Land of Mountains. Already weakened by warfare, the Sons were suddenly struck by a deadly plague in (possibly created by one of the slave clans) that spread rapidly through their ranks due to their self-crafted genetic uniformity. The virulent disease nearly exterminated the Sons and brought the organization to its knees, but the worst was yet to come.
Various factions in the Sons' home village vied for dominance over what was left of the organization and so began a devastating civil war that destroyed all the villages and transformed the surface of their region of the land into chains of islands. The war almost led to the extinction of the Sons' many clans and drove the most of the surviving clans underground where they devolved into primitive tribal clans. Only a faction known as The Elders, who were descended from the priest caste of the organization, recalled the true history and subsequent fall of their people. In the following centuries, the defunct Sons of Darkness was erased from the records of its former slave laborers. It was lost to the pages of galactic history until its rediscovery during the Second Great Ninja War.
During modern times, the Sons of Darkness, or SOD, is a bioengineering group founded by a mysterious group of rouge shinobi. It originally handled normal genetic engineering, such as making miniature elephants, but moved on to something much grander by using rare ninjutsu and sealing jutsu. Sometime in the not-to-distant past, the Sons began construction on an amphitheater in on a group of islands called the Five Deaths, but it was abandoned. Soon, a natural preserve park on Isla Matanceros, 120 miles off of the Land of Mountains, was nearing completion. However, interference from a group of shinobi from Yamagakure 2 caused a shutdown of all of the park's systems, and the genetically created biju ran free. The island was abandoned, and work ceased. It is suspected that eight of the nine creatures created escaped the island.