Short version. Long ago the primordals created life. Forerunners rose up and killed precursors when they found out they were not the inheritors of the mantle. Last surviving precursors turned themselves to dust. Dust was later encountered by human race and used on animals to tame them. Animals turn into flood. Begin flood and human war. Humans glass a forerunner planet when they see the flood has already begun infection. Forerunners, not knowing the flood was present on said planet, take it as act of war and begin forerunner and human war. Pressed on two fronts by both forerunners and flood, humans lose the war thousands of years later Forerunner encounters flood and decides to save human memories for strategy to defeat the flood using the composer Forerunners losing, in a act of desperation and with all other options failed, the bornsteller didact fires halo ring Halo is a super weapon that kills all sentient life in the universe essentially killing the flood food supley and starves them The didact puts a teleporter to the ark buried beneath the earth so man can one day learn its violent histery Millions of years pass and the man has discovered slip space and encounters a religious alien race known as the covenant.