In 2364 Romulan forces confronted the Enterprise-D at the Neutral Zone, the first direct contact with the Romulans in more than fifty years.
After the Tomed Incident of 2311 the Romulan Star Empire withdrew into isolation and had no direct contact with the Federation for more than half a century. In 2364, outposts on both sides of the Romulan Neutral Zone were destroyed, and the Enterprise-D was sent to investigate. A Romulan warbird decloaked near the ship, and its commanders made clear that the Romulans had been watching and were now returning to galactic affairs.
The Romulans had suffered similar losses, and neither side had caused them. The attacks were later linked to the Borg, a threat the Federation would meet in person the following year. From this point on, Romulan intrigue became a constant concern for Starfleet.