The Federation has been in the war since the beginning. The Romulans are late comers.
Barring total victory by The Dominion, in which case no one will really care, at the end of the war (however it may end) the Romulan military would be in better shape than the Federation military.
So as soon as that episode happens you're thinking, "Good for the moment but we know that when the Romulans inevitably find out* the Romulans will go to war with the Federation, win, and make Earth into one of the minor outlying provinces."
But then things go sideways.
The Dominion recruit a powerful ally and the war turns to crap even with the Romulans on the Federation/Klingon/[OMGWTF The Sky Is Falling] side. Why was this ally so powerful? As near as anyone can determine, the entire race is composed of clones of Princess leia who favor the bounty hunter disguise she used at the start of Return of the Jedi.
They're called Breen instead of Boushh, but take a look and you'll know.
And that's when things get really fucking bad from a Romulan Star Empire perspective. The people who end up being their saviors after this turn are the Cardasian resistance.
The Breen are people no one wants to fight, but they're also not great conquerors. In fact, prior to their joining with the Dominion, every time they were mentioned in Star Trek (which happened frequently) it was because people thought they might be to blame for something but they never were.
You don't invade them, you fear them to the point of worrying every time that something goes wrong that it could be a sign the Breen are on the move (which is sort of like the four horseman teaming up with the Fenrir, the Midgard Serpent, Hel, and ... my knowledge of cool end times figures sort of ends with those two mythologies) and they're never actually involved in anything of note.
The Dominion recruiting them was really impressive since they don't tend not to get involved and it's really good for the Dominon's war effort, but it didn't exactly mean that there's a lot of Dominon new allied territory for the victors to divide. The Breen simply haven't been expanding their empire enough for that.
The prize on this side of the wormhole was Cardasian space. With the Cardasian's emerging as the saviors that prize is off the table which means...
All that's left is hoping to get territory on the other side of the wormhole and ... they don't. Not a bit.
After all of the dead Romulans and all other costs of the war the Romulans have nothing to show for it. They don't have new territory, they don't have revenge (the war ended in a peace treaty not subjugation or extermination or some such) they've got nothing but lost lives and lost resources.
The Romulans in charge are going to be called to justify a war that accomplished nothing, and the only thing they can point to is a single assassination and a computer record so beat up it can't be verified to be a non-forgery. If the record is accurate then it was a defensive war and they can justify it to their people ... maybe. But only if they can prove beyond all doubt that it is accurate.
Meaning they need to prove that the (non-existent) meeting the record purported to record really happened and really happened that way and thus the Romulan Star Empire was in existential danger because otherwise the leadership of the Romulan (Star) Empire might as well decapitate themselves to save the inevitable revolution the trouble,
No good came of the war for them. They would have been much better off to sit it out and then, if it proved necessary, take on whatever war hammered powers came out the victors. Instead those who run the empire find their hands drenched in Romulan blood and Romulans are nothing if not passionate.
The friends, family, and lovers of the dead are going to want those responsible to pay.
Thus the Romulans need to prove that they didn't go to war on inadequate evidence and they need to prove that the fake meeting happened and the dominion was responsible for the death of Vreenak.
Or at least they think they do.
And it shouldn't be too hard. If the record is accurate than there would be mountains of supporting evidence and the wonderful beautiful part is that, as a result of how peace came about, they can simply go to the Cardasians and the Dominion to get the damn records. The Cardasians switched to their side. The Dominion has a peace treaty with them.
Except doing that will prove that it didn't happen which then means that the Romluans need to find out who set them up. They need to otherwise, best case scenario, the entire leadership is kicked out of positions of power. Worst case scenario the streets are stained green with their blood and the blood of everyone they ever associated with.
At this point it isn't even about the truth, though they'll probably learn the truth. They need a scapegoat if they can't learn the truth, and this is where it gets fun.
The only logical scapegoat is Deep Space 9. Even if they think they're lying to cover their asses, they'll actually be telling the truth: The Federation, specifically via their lies and manipulation, is responsible for the death of every Romulan lost in the Dominion war.
And this then raises the potential for the ultimate save for the rulers of the Empire. The Federation has been getting their asses kicked. For a long damn time. They're worn down, their military is worn out, and the Romulans have the upper hand in all imaginable ways. (The Federation has all of one cloaking device, and that difference is just the start.)
And they'll be without their allies. Klingon honor wouldn't let them side with the Federation anyway once the truth came out (even though they would have appreciated the help it provided in the war) but Klingons have a particular aversion to assassination via bombs. It's not quite a religious conviction, but in some ways it's even stronger.
Blowing up Vreenak was basically the ideal way to convince the Klingons not to side with the Federation in the inevitable Federation-Romulan war.
Going to war as a response to a war you shouldn't have gone to might not seem like a good strategy but it will provide everything the Romulans need to maintain their stability.
They need loot. Territory, treasures, the spoils of war. The Federation has it (right next door no less.)
They need vengeance. All of the Romulans in the Dominon war died for nothing and if the outrage of that isn't channeled outward Romulan society will probably self destruct. Since the Federation is responsible for the Romulans being in the war, and they did it just because the were willing to trade Romulan lives for a marginally better position in the war (so extra emotional resonance points) they're perfect.
They need to prove that they can still win wars. Not tie them, win. Come out the victor, gain new territory, expand the empire. The low hanging fruit that is taking over the Federation will provide that proof.
So on, so forth. War with the Federation is an answer to every problem.
The only thing that could save the Federation is if someone were to, say, blow up the Romulan sun and destroy one of their home worlds in a movie that started an execrable series intent on destroying all your dreams and turning people of color into Benedict Cumberbatch.
But let us say that didn't happen. War between the Romulans and the Federation is inevitable.
And that war should be very interesting.
Especially, and this is important, the Romaulan politics going into it.
The top of the leadership needs to be able to tell the people who is to blame and, since the Federation really is to blame, that's already a reason. They also need to prove that they're still an imperial power. They just went to the biggest war they've been in in ages and they didn't expand their territory or get any loot.
They need to show they can do that otherwise they'll lose their power.
Others have historical reasons for wanting to take down the Federation. Romulan Wars aren't supposed to end in peace treaties and neutral zones which means that for 200 years Romulans have wanted to get back at Earth. More than that the Federation is literally the anti-Romulan coalition.
When the Earth-Romulan war ended the people who banded together against the Romulans decided to turn their wartime anti-Romulan alliance into ... well, the United Federation of Planets.
The Federation is seriously the Anti-Romulan league. There's probably a bit of resentment.
But there are also going to be people who have had their fill of war.
There are Romulans who might want to normalize relations. There have always been Romulans who supported reunification with Vulcans anyway and right now their economy could probably really use new trading partners.
And there's also the Steve Rodgers / Tony Stark split. Vulcans and Romulans are two different races of the same species and that species has massive anger management problems.
Their emotions can be explosive and Vulcan and Romulus both had to find a way to not wipe themselves out with that shrapnel.
If you watch the scepter scene from The Avengers you've got sort of a human example of what happened.
Banner needs to not emotionally explode. Rodgers says you need suppress, keep emotion entirely under control of your rationality. That's the Vulcan way. Stark suggests a different approach. Let off steam so it doesn't build up until it explodes. The Romulan way.
Romulans embrace their passions and thus by letting their emotions out they generally don't explode.
After the Dominion War, though, their passions should be boiling.
And then there's just the ordinary scheming that happens. People who feel they can profit from war, people who think they can use the whole volatile situation for personal or political gain. Trying to get someone you have a nice old bloodfeud with labeled as a Federation collaborator.
Also there's a question of what the war is going to be about. For the Romulan government it's going to be best for it to be a war of conquest, but for those who lost loved ones for no reason other than Federation lies, extermination might feel more appropriate.
Trying to control and channel the anger and hurt into something that's productive for the Empire (the Romulan way of dealing with the Romulan-Vulcan emotional problems writ large) is going to be a difficult and complex task. If it can be managed.
If it can't, then the war will spiral out of control.
-Thus the proposal for fan fiction. We know the Romulans and Federation would be going to war, we know the Romulans would have the extreme advantage, what we need is for people to tell that story.
Or rather... those stories. The lead up to war, the war itself, and everything after the war would all be full of stories.
- - -
* Even if the cover-up were perfect which would sort of be like ... ok, I can't actually think of anything unlikely enough to compare to the suggestion that it's even possible to believe that the Romulans might not find out every detail of Vreenak's death in the post war galaxy using only ordinary means.
Did you know that falling up is actually within the realm of physical possibility? The only reason that it doesn't happen is that the probability is negligible. Even if some of the particles that compose your body did tend towards that end in spite of the massive probability against them, the vast majority would follow the much more likely path that gravity suggests: down.
Are you more likely to fall up the next time you trip than the events of In the Pale Moonlight to remain a secret? Of course. But you're so much more likely that the comparison doesn't even make sense. It's like saying that the sun is more likely to come up than it to turn out that everyone in your life is actually a mutant lizard person who has been tricking you into believing that humanity is a thing as part of a massive universe spanning --most of the stars are just lights suspended in the geodesic dome around the earth in this scenario, but the universe is actually larger and space is, at the non-solar system level, more hyperbolic than Euclidean, and don't even ask about the speed of light because you don't want to know-- plot to create intelligent cheese.
Is it true? Yeah, the sun is more likely to rise when it normally does than ... that other thing. But the scale is just so different.
So, the point here, is that we know that using only fairly straightforward means the Romulans will find out. The odds against it aren't merely too great to calculate, they are too great to imagine. The human mind lacks the capacity.
But, if it didn't...
. . .
in that extremely unlikely event, time travel has been used as (an extremely mundane downright boring and routine) method of fact finding for over a hundred years by the time of the episode in question.
It's only used to find information about events in your own history because if you get caught in some other power's history then they'll kick up the time travel and start visiting your history and at that point there are only two options:
- Time War. Even if your empire survives it is exceedingly unlikely that anyone you know or care about (yourself obviously included) will exist when the war is over.
- Temporal Cold War. You don't even want to know. Trust me on this. I stuck with Enterprise way too long in hopes that it would get good.
But important events in your own history you check out using time travel, and after the end of the Dominion War the Romulans are really, really going to want to prove that the casus belli justified the cost which means that they have to investigate everything that happened surrounding Senator Vreenak's assassination down the position and velocity of individual subatomic particles.
"Can't be done," you say? Heisenberg compensators.
Plus, let us never forget, the Romulans create and ride black holes (every TNG/DS9 Warbird has one) more or less for shits and giggles. The founders of Time Lord society on Gallifrey had mind-rending, eternity-lasting, reality-tearing trouble with the whole black hole making process.
We don't know if their ships are bigger on the inside or not, but it hardly matters. Using time travel to investigate important events in your own history, like say why you went into a costly war, is old technologly. It is to them what 1909 technology is to us.
All that they need to do to find out what really happened to Vreenak is have a war free time (you do not want to fuck with time travel during a war) and be willing to deploy technology no more advanced to them than a shortwave radio is to us.