The Great Wars are a fictional conflict from the Shannara series by Terry Brooks.
According to legend, the Great Wars were a result of several things. These things were common to most societies: territorial dispute, political disagreement, and so on. With the publishing of Armageddon's Children, it is revealed that Demons serving the Void (the collective embodiment of evil) started the Great Wars.
The wars became extremely serious when they broke into full scale combat. The uncontrolled energies unleashed by the sciences Man had developed over the years tore across the earth, drastically altering the landscape and killing most of the life in the world. However, during the events of The Genesis of Shannara, a band of Humans, Elves and other creatures and animals managed to protect themselves from the devastation of the outside world. The Wars had caused such upheaval that Man had divided into four races, only one of which remained seemingly unchanged. The rest, however, were different.
One race had fled beneath the surface of the earth to escape the effects of the Great Wars. Thus they became accustomed to underground life, their eyes adapting to darkness while their bodies became short but strong. When they emerged, they were nearly blinded by the light of the outside world. Because of their new appearance, they were called Dwarves, after a mythical race of the old world.
The origin of the Gnomes is not explained, but that of the Trolls is. Survivors of the war living in the mountains were mutated by the energies unleashed in the conflict, becoming large and powerful figures. Their skin became tough and bark-like, and they were known as the Trolls.
For a thousand years after the Great Wars, these races struggled to survive. Then Galaphile, a wise man from the reemerging Elf race, gathered the greatest minds of the races at Paranor, thus bringing an end to the turmoil. The Elves are in fact not human mutants but instead Faerie creatures of a lineage older than humanity, though they have become mortal and are commonly mistaken for another human-derived race.
Despite the destruction of the old world, some elements survived. Among these were bits of the old sciences passed down by the Druids, some of them kept by Cogline. Other survivors included Antrax and its creations in Parkasia, and a few ruins of that age existed as well. Also in Parkasia lives a race called the Rindge. They are described as having a copper-ish color and speak an ancient Dwarf tongue.