The Second Klingon Empire was a period within Klingon history which ran between 2069 to 2369. (Decipher RPG module: Worlds) The start of the Second Empire began after the death of the last Emperor of the Klingon Empire in 2069 which led to a brief civil war. This act resulted in the dimishment of the Emperor's power and the rise of the prominence of the Klingon High Council. In addition to this, the first Romulan-Klingon War ends at this time. (ST reference: All Our Yesterdays: The Time Travel Sourcebook)