system
Given the following post, respond as if you're commenting on Reddit:
human
[Halo] Why did the Prophets go through all the trouble of instigating a crippling civil war at what was probably the most vital moment of their campaign against the humans?

I get that they were trying to phase the Elites out with the Brutes but.....why the sudden mass murder? Were the Elites not loyal, capable soldiers who had lead a very successful war against the UNSC? Why not try to slowly and safely give the Brutes more and more power instead of declaring open war against roughly half the population of the covenant seemingly out of nowhere?
gpt
1. The San 'Shyuum were arrogant. The Sanghelli were becoming more suspicious of why the humans were not offered to become members of the Covenant. The Prophet of Truth believed that his plan to exterminate the galaxy of all sentient life would not fail, hence increasing the need to replace the Sanghelli before they can rebel at mass genocide.

2. It was not a successful war as you might think. Often times, the UNSC were able to push back the Covenant on the ground. If it were not for the superior tech of the Covenant ships, Humanity would not have lost as many colonies as you might think.

3. There was still lingering feelings between the San 'Shyuum and Sanghelli. The San 'Shyuum were still smarting from losing the ground war against the Sanghelli. Also, despite the centuries of the Covenant, the San 'Shyuum never did quite trust the Sanghelli. The Sanghelli were too questioning, too independent, a little too much a painful reminder that the San 'Shyuum lost to them when they were still martial race.