How did the Wraith defeat the Ancients?
The Wraith were able to defeat the ancients because of numerical superiority. Whilst a single Ancient Aurora-class Battleship could take on several, if not a dozen Wraith Hives, the Wraith just kept sending more and more. The actual conflict was a battle of attrittion in which the Wraith took worlds one at a time, until only Atlantis was not subject to the Wraith. After a prolonged orbital bombardment, Atlantis was finally abandoned. The sheer quantity of Wraith warriors and ships lie in the organic nature of the Wraith. A drone is “born” fully matured and ready to fight. This lack of nessesary training, combined with the ZPM-powered Wraith cloning facility, allowed the wraith to replenish their horde as quickly as any were lost. Also, the organic nature of their ships meant that no time or resources need be wasted on ship construction, as ships can be grown in numbers limited only to the raw biomatter available in the area.