The Forerunners had a Tier 1 level of technology. So I have to ask. Why is it that they had such a hard time combating the flood? The forerunners had the technology to create vast armies of fully mechanical warriors to fight for them. They had warmachines that could raze an entire continent with ease. They had highly advanced armored battlesuits that could make a single soldier almost as powerful as Master Cheif. They had some of the greatest minds in the world, with some being centuries old and with a wealth of knowledge not only in science but also in other matters like maybe warfare and weaponry. They would also have some of the greatest and most powerful space fleets in existence, with perhaps hundreds of thousands of capital-sized ships at their disposal that could incinerate the Covenant Empire with relative ease.
So WHY did the Forerunners have such a hard time beating them when everything that could be HIGHLY effective against parasitic organisms (automated mechanical army, Weapons of mass destruction, armored battlesuits) was in their favor.
Did any of the books ever explained this? This is always something that bugs me to no end....