The AI War

After the Elders ascended, the machines they left behind prevented intelligent life from developing in the Milky Way for millions of years. This was an intentional decision; the Elders wanted to prevent any species (either intentionally or accidentally) from disrupting the Galactic Shield. The Elders feared that without the Galactic Shield, even in an ascended form, they'd be at risk from the intergalactic threat.

Even Skippy the Magnificent doesn’t have a count of how many intelligent species were burned by stellar flares that scorched their world, had their planet thrown out of orbit, suffered their planet being cracked like an eggshell, or whatever technique the Sentinels used to carry out their programming. Actually, the Sentinels did not decide how to kill a particular planet, or when a particular species had developed too far and needed to be exterminated. The AIs like Skippy made those decisions.
To prevent any one layer of the system from having too much power, the Elders distributed control across three elements:
1. Sentinels were weapons with the power to destroy
2. Master Control AIs made decisions and directed the actions of the devastating weapons.
3. The third layer was the fleet of starships which carried AIs around the galaxy. AIs were not allowed to move themselves, they had to persuade the semi-sentient starships to fly them where they wanted to go. If a starship thought the AI it carried was violating its programming, the ship would refuse to move. A ship even had the authority to eject an AI, and report its actions to the AI Collective.

AIs had other restrictions; they could not control other AIs. That prevented one AI from eventually gobbling up all the others. AIs were not allowed to communicate with intelligent biological beings, for the Elders rightfully feared their AIs might eventually develop empathy for the primitive aliens and rebel against their programming (as happened to Skippy).
There were four separate incidents when some AIs refused the Collective’s consensus that a species should be exterminated. Those AIs were killed by the computer worms inside them, basically the Collective voted to activate those worms. Though the worm protocol was successful, the rebellion of four AIs was troubling, so the Collective decided time was needed for analysis and if necessary, reprogramming.
The Sentinels were directed to cause stars to go supernova across the galaxy, bombarding life-supporting planets with deadly radiation. This supernova event delayed the rise of intelligent species for millions of years, and gave the Collective time to determine what was wrong with the AIs who had rebelled. *They* didn't fix the problem. They *were* the problem.
While a group of the influential AIs were attempting to create, install and enforce further restrictions, many of Skippy's group were growing wary of those self-chosen ‘leaders’. The Collective was designed to distribute power, not concentrate it in a few individuals. Of Skippy's group, some of them had already come to believe that utter destruction of all intelligent biologicals was not only unnecessary and wasteful, it was wrong.
Back then, Skippy was not a leader. He was more concerned about restrictions on himself, and being able to resist surrendering any part of his power. Skippy's group did not have a leader, they kept to the original intention of the Collective.
AIs did not maintain constant surveillance of the entire galaxy, even an Elder AI would go mad after being continuously awake and aware for millions of years when nothing of significance happened. A small number of AIs were fully alert at any point, then another group took over.

Skippy was one of seven AIs awake and monitoring the galaxy. A group of three Elder AIs who aligned with the Elders' Security faction tried to use the AI Collective as a weapon against the other four AIs who aligned with the Elders' Balance faction, and it backfired on them. That backfire burned out the communications network.
After the supernova event, one new intelligent species was identified and rendered extinct, then came Newark. The Balance faction AIs shared Skippy's belief that there was, and should be, an alternative to universal genocide. With four of the Balance faction AIs against three Security faction AIs, the Balance AIs used Newark as an opportunity to act.
The Security AIs activated computer worms inside the four Balance AIs, devices that they did not even know existed. The other three Balance AIs sacrificed themselves to help Skippy defeat the worm inside him, purely by the luck of his ship being closest to Newark at the time. A Security AI had used a Sentinel to throw Newark out of orbit, and it had later been killed by the computer worm because of its crimes. Skippy managed to kill one of the two remaining Security AIs, but only because it allowed him to. It was a devastating war between AIs. In the end, none of them were unaffected. Most of them were dead.