The Attack on Mars was an attack by A500 android worker units at Utopia Planitia Ship Yards on the Martian colonies and the Utopia Planitia Fleet Yards itself.
On Aia, Tal Shiar/Zhat Vash General Oh showed several members the "Admonition". Only Colonel Narissa and her aunt Ramdha survived. Narissa and Oh agreed to put an end to the Federation's synthetic life-forms. Thus, decided that Mars would be perfect target.(PIC episode: "Broken Pieces")
When it was discovered that Eisn was going to go supernova and destroy Romulus, the Federation offered to assist in the evacuation of nearly one billion Romulans within the blast range of the supernova.
They began constructing a fleet at Utopia Planitia Ship Yards to evacuate Romulans to safe locations.
Attack on Mars
The attack occurred on First Contact Day, 2385. Synth-controlled ships began bombarding the Martian colonies and attacking Utopia Planitia Fleet Yards.
Following the conclusion of the attack, 92,143 had been killed and the whole of the Romulan rescue armada and Utopia Planitia Fleet Yards had been destroyed. In addition, the attack ignited vapors in the Martian atmosphere, which continued to burn as of 2399.
Immediately after the attack, all synthetic life was banned by galactic treaty. In addition, the Federation refused to undertake any further attempts to rescue the Romulans - 14 species had, prior to the attack, threatened to withdraw from the Federation.
Admiral Jean-Luc Picard had developed an alternate plan to rescue the Romulans, and presented it to the Federation Council, stating that they would either accept his plan or his resignation. After the meeting, he informed Raffi Musiker that they had accepted his resignation. His resignation directly led to her being discharged from Starfleet, leading to her harboring a 14-year-long resentment towards the former admiral.(PIC episodes: "Remembrance", "Broken Pieces", "Et in Arcadia Ego")