A rogue synthetic attack on the Utopia Planitia shipyards on Mars.
In 2385 the Utopia Planitia shipyards on Mars were building a fleet of rescue ships for the Romulan evacuation, with synthetic workers doing much of the labor. These synthetics were widely trusted, and the project was seen as a symbol of the Federation's humanitarian mission.
Then a group of the synthetics turned on their creators, hijacking the facilities and causing a catastrophic firestorm across the Martian colony. The event was a profound shock. Many people in the Federation had come to believe in the safety of such technology, and the sense of betrayal was intense. Mars lost its shipyards, its population suffered terribly, and the fire cast a long shadow over Federation life.
The consequences were far-reaching. The Federation Council reacted by banning synthetic life, and the Romulan rescue effort was cancelled. Jean-Luc Picard resigned from Starfleet in protest, and his life took a different path as a result. Years later, the disaster remained a raw wound and a political flashpoint that shaped the events of Picard's final adventures.