Ages of Conflict
From Halopedia, the Halo wiki
Covenant history
The Age of Conflict would have happened many thousands of years after the Age of Abandonment. It is believed that in this Age the Elites and Prophets began fighting each other. It is not yet known why the war started. This Age may have lasted for thousand's of years, because the war went on for an extremely long time, but it definitely would have ended with a truce, when the prophet's told the Elite's of the Forerunners.
Note: There could be several Ages of Conflict. If there are, they would have presumably been created upon some major new development that influenced the war.