AboutThe incorporation of the Cole Protocol slowed the Covenant advance, but they continued to attack and glass human colonies nonetheless.
Middle Years (2535 - 2550)
The first ten years of the war saw the Covenant wipe out a large number of outer colonies. While the UNSC threw everything they could at the alien fleets, they stood little chance against the technologically and numerically superior force. Only the near-mythic Admiral Preston Cole managed repeated victories, and those only slowed the Covenant's push into human-occupied space.
Facing the fear of total annihilation, the UNSC finally formally incorporated the Cole Protocol, an order that tried to ensure the Covenant never learned the location of other human colonies through the capture of UNSC ships and AIs. While it was effective, the fact that the UNSC waited ten years to enact it allowed most of the outer colonies to get wiped out, and left a sour taste in the mouths of colonists who thought the UNSC let the Covenant destroy the Insurrection-friendly outer colonies. The next fifteen years saw a considerable slowing of the Covenant advance, but even so, humanity slowly lost world after world, and eventually were left with only Earth, the inner colonies, and a very small handful of outer colonies.