Attack on Mars and the Synth Ban

In the 2380s the Utopia Planitia shipyards on Mars were building the vast armada meant to evacuate the Romulan people before their star exploded. Much of the labour was done by synthetic workers, androids derived from Data's design but without his consciousness.

On First Contact Day 2385, the synths suddenly turned on their surroundings, disabled the planetary defences and directed them against the shipyards. The fleet under construction was destroyed, 92,143 people died, and Mars was left burning for years. The cause of the uprising remained a mystery.

The Federation responded by outlawing all synthetic life and abandoning the Romulan rescue effort. Jean-Luc Picard, who had led that effort, resigned from Starfleet in protest. Years later it emerged that the attack had been engineered by the Zhat Vash, a secret Romulan order determined to stop artificial life, through an agent in Starfleet Security, Commodore Oh.