The Khitomer Massacre was a Romulan attack on the Klingon colony on Khitomer in 2346. This was achieved when a Klingon traitor provided codes to the Romulans. Almost all of the 4,000 Klingon colonists were killed. Worf, son of Mogh was one of the few survivors. The USS Intrepid provided support and humanitarian aid, which in turn helped bring about the Treaty of Alliance. (TNG episode: "Sins of the Father", ST - The Lost Era novel: The Art of the Impossible, Last Unicorn RPG module: All Our Yesterdays: The Time Travel Sourcebook)