For the Romulans, it started when Federation ships began to treat the Rihannsu border as a mere suggestion. More and more Federation ships were being spotted in Rihannsu territory, and the responses from the Fed captains, when hailed with warnings, were becoming increasingly beligerent.
Tensions mounting, and diplomatic parties on both sides wishing the transgressions to stop, a meeting was scheduled on SB1. The Romulan envoy, consisting of 5 members, met with what appeared to be 20 or more of the Federation personnel. The meeting did not go well, and the Romulans left as though precious time had been wasted for idle banter and nonsensical accusations. The purpose of the meeting was to gain confirmation from the UFP that they still recognized the Romulan-Federation Border Treaty, and eventually receivd this. They were also assured that the UFP would keep a better leash on their vessels (more specifically their commanders), and not cross into Romulan space again.
They lived up to their promise, for a whole week. First one ship was seen, then the USS Exeter on two seperate occasions. When questioned, the Federation gave some excuse about it really being Federation-style ships from some Mirror universe, but the Romulans wouldn't buy the story.
The final straw was when Riov S'Kard tr'Vriehu and Riov Hua t'Annhwi stumbled upon the USS Banneker in Romulan Territory. The vessel and it's crew were captured, and brought back to the ChH Rokhelh'Ael. Although the crew were released later on good faith, the vessel remained a posession of the Romulan Galae.
Shortly there after, the Romulan Government received a notice from the UFP. A proclamation of war against the Romulans. Romulan vessels headed for the border and waited. And waited. And waited some more. Nothing came for them. Eventually Romulan ships got tired of waiting, and proceded into Federation space to meet their foes. Only one was found, and after a few blasts from the ChR Hvei'knenn, the Federation ship retreated to the safety of StarBase1.
As the Romulans soon found out, there was a reasom for the awkwardness that the Federation pursued their own war...for they had simultaneously declared war on the Klingons as well. Although it was difficult to draw vessels out from the protection of the Federation's starbase, the Romulans continued trying for several weeks. At one point the ChR Hvakh approached the starbase to find a Federation vessel out from it's cover, and in an intensive disagreement with a Klingon vessel. The Romulans watched from nearby, curious to see what the Federation's tactics were. As expected, the vessel simply tried to repeatedly lure the Klingons in to range of SB1, but rarely was it long enough to receive much damage. The Romulans once again decided to take some shots at the base, in case they could get lucky, but eventually dragged themselves home as the Klingons did.
For the Romulans, the war was not much of a war. The Federation refused to engage their vessels when the opportunity arose, and the Romulans grew tired of attempting to take SB1. Returning to Romulan space, they waited. Again, nothing came to them however, other than news of the Klingon blockade of Vulcan, and rumours of an apparent success by Klingon forces to take out one of the Federation ships.
Eventually, apparently a new group of personnel took over leadership of the UFP, and requested an end to the war. The Romulans, almost laughing this off, agreed, and repiritions were arranged. The details of which have been forgotten, but the Romulans ended up returning the USS Banneker, and received technologies from the Federation (including the tricorder upgrade), among other things.
Life went on, and the Universe simmered down to a mild yawn.
<I'm sure some of the Feds or Klingons around at the time can fill in details from their sides>