The Tomed Incident and Romulan Isolation

The Tomed Incident of 2311 was a violent clash between the Federation and the Romulan Star Empire that cost thousands of Federation lives. Canon offers few details about what actually happened; the event is known mainly through later references by Starfleet officers, who treat it as a defining moment in relations between the two powers.

In its aftermath the Romulans withdrew behind the Neutral Zone and cut off nearly all contact with the Federation. The Treaty of Algeron, which reaffirmed the Neutral Zone and barred the Federation from developing cloaking technology, belongs to the same period of settlement, although the screen never states exactly when it was signed.

The Romulan silence lasted more than half a century. It ended in 2364, when Federation and Romulan outposts along the border were destroyed by an unknown force and a Romulan warbird confronted the USS Enterprise-D in the Neutral Zone. That encounter marked the Romulans' return as an active rival, ushering in decades of espionage, proxy conflicts and uneasy diplomacy.