In 2366, the USS Enterprise-D was investigating a temporal rift. While examining the anomaly, the USS Enterprise-C emerged, resulting in an altered timeline where the United Federation of Planets was still at war with the Klingon Empire. This timeline was supposedly destroyed when the Enterprise-C went back through the rift, but the Enterprise-D experienced a core breach that was induced by Klingon attacks. The breach cause a divergence in the timeline, and the Breached Reality was formed. TNG: "Yesterday's Enterprise"