Here's what I was told; 343 guilty spark was lonely, so he decided to build a sentinel army, he then released the flood so he could have his own little mini war he could enjoy. He started blowing up installation after installation, releasing and freeing the flood. Then he wanted a giant battle with the flood, then the humans came which was what Halo CE came about. He was happy to see them knowing they are reclaimers, They wanted to destroy the halo and 343 GS wanted to fire it, but he wasn't allowed to, it had to be activated by a relaimer, or any other status.
I do not know if this story is true or not, but this is partial of it. Can anyone tell me if this is right or wrong?