User blog comment:James12708/Reapers VS. Forerunners VS. Angels from Darksiders VS. Humanity from Halo VS. Council and humanity from Mass Effect VS. Imperium of Man/@comment-50.80.96.33-20130222012310/@comment-1786741-20130222021020

There are a couple reasons the Forerunners were defeated by the flood. First of all, they had just finished with a costly war against the humans. Second, most of their weapons were made to fight synthetic enemies and such, they weren't prepared for the Flood's unique biology and tactics. The Reapers wouldn't have time to adapt or harvest anything, or even if they did manage it would never be enough to effectively combat the Forerunners as they would be INSTANTLY obliterated. Either way, the Reapers will always lose against superior tech, weapons, numbers, and defense. They have no chance whatsoever, get over it.