Ages of Doubt
The Ages of Doubt were eras in Covenant history where the effects of internal or external conflicts are dealt with. The last Age of Doubt, the 23rd, succeeded the 39th Age of Conflict, when the Unggoy Rebellion destabilized the Covenant, and lasted until the discovery of the Reclaimers (Humanity) and the deposition and replacement of the Hierarchs. This age was succeeded by the Ninth Age of Reclamation in 2525.
Progression of the Ages
Leader, or Chieftain: Doubt.
In Halo Wars, when playing as the Covenant, players can upgrade their Temple by researching the Age of Doubt, improving all Covenant technology by 1. Advancing to the Age of Doubt also gives Covenant players the ability to make Type-30 Locusts, Vampires, and many other types of units.