Anywho, that aside, the below is the premise text I've come up with:
The Klingon Empire and Gorn Hegemony have been in a state of Cold War with each other since 2376, when the Gorn positioned the bulk of their forces along their closest border to the Klingons, and the Klingons in turn began focussing their post-war rebuilding in the region. Once the Empire had restored their forces to their pre-war height by the end of 2385, Federation diplomatic intervention was the only thing preventing the Klingons from launching a full on war against their Gorn neighbours; the Gorn were neither willing to back down from their stance, nor did they possess the military might to launch an offensive themselves; the two powers were essentially locked into a stalemate, and conflicts and skirmishes between independent Klingon and Gorn vessels in the area of space that separated the borders of each power became more frequent and violent.
Following the Hobus disaster which took out several starbases and caused severe damage to the Romulan Homeworld in 2388, the Federation requested the Klingons join them in providing assistance to the beleaguered interstellar nation; a request which the Klingons pointedly refused. When the Klingons sought to take advantage of the Romulan's disarray and tried to reclaim worlds that the Romulans had taken from them a century previously, the Federation prevented it. As a result, political analysts have described the tensions between the Klingon Empire and the Federation of Planets as unsteady and strained as it was before the Klingons last withdrew from the Khitomer Accords in 2372.
Despite this, the Gorn know that the Klingons would still ask the Federation to come to their aid if they were ever to be attacked. Keenly aware of the vast size of the Empire, the Gorn also know that it would only be a matter of time before the Klingons were able to amass enough forces to defy the Federation's diplomatic restraints and launch their own offensive on the Hegemony. And so they sent out ambassadors to those powers they know would have no moral compunction against joining a fight against the Klingons; the Romulan Star Empire, the Tholian Assembly, the Breen Confederacy, Tzenkethi Coalition; even the Rhitorian Confederacy. While many of their overtures went unanswered, not all of them did.
In July 2391, a Tal Shiar operative arrived in secret on the Gorn homeworld for a meeting with the reptilian leadership. The deal was struck out very quickly; the Romulans would covertly assist the Gorn through their intelligence service, providing supplies and tactical assistance in return for undisclosed future favours to be called in by the Romulans at a time of their own choosing. They would also provide assistance to any other powers who would provide the Gorn with military assistance, enabling them to make their way unhindered through Federation space to join the Gorn forces, without having to spend months on a long journey through outlying neutral space. With this agreement in place, the Rhitorians and Tzenkethi agreed to an alliance with the Gorn, and began covertly sending ships to rallying points within Gorn space, utilising loaned Romulan cloaking devices to move through Federation space, free to move without fear of detection as the only tachyon detection nets the Federation had set up were along the Romulan border itself.
In October 2391, the combined Gorn/Tzenkethi/Rhitorian forces launched an attack on the Klingon worlds of M'Char, B'rel and Q'tahl, taking them by surprise thanks to intelligence provided by the Tal Shiar forward scouts. Ogat was the next world to be captured by the quick-moving combined forces, falling before the Klingon High Command had received the news and issued orders to their commanders to launch a counter-offensive. An hour later, the Palais de la Concorde on Earth received a request from the Klingon ambassador for assistance, and Starfleet's 11th Fleet out of Cestus III was ordered into action, with reinforcements being provided by the 6th Fleet out of Starbase 311.
(As a note, using our current 2RL years to 1IC year ratio; we're in the latter half of 2391 right now; in January 2016 we'll move into 2392. Just to make it clear that October 2391 doesn't necessarily correspond to October 2015)