There’s some debate about whether the Precursors planned to destroy the Forerunners or if the Forerunners attacked unprovoked. Believing they were the superior creation, the Forerunners obliterated the Precursors and took up the Mantle of Responsibility for themselves. The Precursors had apparently decided to pass the Mantle onto the humans - letting them dictate the flow of life in the universe - rather than the Forerunners. In the Forerunner-Precursor war, the Forerunners destroyed their creators. They’re not all evil, but they are primarily responsible for nearly every problem in the Halo universe: the Flood, the Halo rings, and - to some extent, out of their control - the Covenant itself. They were positioned to be the Precursor’s original successors, and, at one time, the most powerful species in the universe. The Forerunners were humanity’s biggest rivals and serve as the primary antagonists in 343 Industries’ Halo games. The Precursors helped shape and evolve humans, the Forerunners, and many other races using the Mantle of Responsibility, a creation philosophy. The Forerunners get all the credit in the Halo games, but the Precursors came before, as their name implies.
