idk

Forerunners were the masters of technology: AIs, computing, and non-biological instruments, with the Composer they could transform life in technology, the Halos could destroy all life in the galaxy,etc. Precursors were the masters of the physical form, of biological life, everything they made was alive, they could even create life.They were the ultimate rulers of everything. The only reason the Forerunners defeated the Precursors was due to their excelling at destroying life which is the exact opposite of what the Precusors do. The Precursors knew this so before they went "extinct" they created the Flood as a test to see if they were "worthy of the Mantle". They were'nt. The next in line to "be tested" is humanity. Which is why this is the Reclaimer Trilogy. This is also one of the reasons the Librarian accelerated the genetics of Master Chief because in the terminals it was said that had the Didact not killed most of ancient humanity they would have eventually surpassed the Forerunners. Thus it would make sense that the Flood would reappear to truly test humanity. Which I can imagine will really **** for us.