This detour into matters of war and destruction is quite appropriate actually, since I'm starting the six book series dedicated to the build-up to war between the Klingons and the Federation.

I recall that sense of looming disaster being quite pronounced in the later books.
Indeed, why it was that the Breen, having taken out Earth's defences, didn't just ram their ships into the planet (rather than floating dreamily through the air spitting out torpedoes on San Francisco as they did) is presumably because they weren't mad enough to commit to more than a "bloody nose"; they must have long-term plans for cultural and economic dominance that won't be served by having everyone view them as mad dogs who destroy whole worlds.
DaveGalanter portrayed in
Tales of the Dominion War - "Eleven Hours Out" that the Breen attacked San Francisco with only 3 vessels slowly and with rather weak weaponry for 11 hours in order to psychologically terrorize the Federation. Also, more powerful weaponry would have been too difficult to sneak past Federation checkpoints.
I'd forgotten it said that, though it makes sense on multiple levels. Yes, it's certainly the case that the Breen's overall intent was to defeat Federation morale and sow terror. Any actual destruction of assets was secondary. It reinforces the sense that warp-capable societies, even on those occasions that they commit to overtly aggressive warfare, still operate within a political ecosystem and act accordingly. Humbling worlds like Earth would pave the way (the Breen hoped) for Breen economic and political gains; destroying them would surely just shock and outrage every civilization that feared it would be next.
(I would say that the Dominion is also unlikely to appreciate the disorder that comes with excessive and unnecessary destruction, but of course Cardassia would glare pointedly at me. Still,
that order came from a sick and thoroughly frustrated Founder who hadn't linked in weeks, was by her peoples' standards therefore extremely isolated, had simply had enough of all these solids making her life difficult and was spitefully motivated as much as anything. On the other hand, the very fact that the Dominion is used to being unrivalled in its home region means that it can afford a policy of extermination. Then again, the honouring of the peace treaty with Bajor, etc., shows that the Dominion is good at playing the game; its whole manner of attack in the Alpha/Beta Quadrants was attempting the political isolation of other nations so that they then had, presumably, no real choice but to accept their incorporation to the Dominion on threat of Jem'Hadar. In other words, replicating among the larger empires the policies the Dominion uses on small nations, where violence is implied and secondary, ideally non-existent, and so long as you shake the smiling Vorta's hand and sign on you get to trade with other member worlds and, more importantly, the Jem'Hadar glaring stonily at you from the back don't get unleashed. It was just the Federation and Klingons being stubborn and "unrealistic" that forced the Dominion to actually resort to large-scale violence).
Still, the Breen. If they can make their point and destroy the sense of invulnerability held by those in the Federation core, then they've triumphed. They'd even earn points among other Dominion-allied nations like the Miradorn, who would be glad to see the Federation a bit bruised, and they won't have crossed any lines that would make them too many enemies.
The Romulans of the 22nd Century, with their hot green blood aflame, seem to be one of the rare exceptions. That's what makes Vulcanoids unleashed so dangerous - they're not, by the usual standards, sane.
I'm not sure about that. In the astropolitical environment of the time, Romulan attacks did achieve their goals. They did prevent a potentially technologically superior Coridan from joining the Coalition; they did permanently destroy the Haakonan threat; they did demonstrate to everyone with the example of Draylax that ignoring Romulan warnings was a terrible idea. If there had been only a bit more paralysis on Vulcan in the last months of the Earth-Romulan war, the Romulans would have been in a position to determine the fate of this whole region of the galaxy. With such examples and no one in a position to oppose them, what would have stopped them?
You make a very good point there,
rfmcdpei. You're right, the Romulans did have achievable political goals in mind and their actions, however extreme, were often geared strategically toward achieving them; successfully, at that. Then again, I'd still say they weren't exactly being sane. They're not thoughtless berserkers - part of what makes Vulcanoids so dangerous is that they're incredibly intelligent, and politically astute. But the Romulans of this era - perhaps again because they weren't part of an established community of powers and thus had no-one to apply the breaks on their excessively bloodthirsty mores, were behaving in a manner that seems very out of place in this universe. I suppose the willingness to employ such insanely destructive tactics is itself a useful political weapon if wielded correctly, and I think you've made a good case there that the situation was such that the Romulans' actions were "reasonable" enough in light of their aims, but I can't call them sane, especially when it led to things like dumping civilization-killing viruses on their enemies with no real care for the possibility of blowback, either natural or political. There's something about Vulcanoids in full on aggressor mode that's removed from other humanoid peoples, and I think that's long intended to have been the case.
Speaking about the Klingons, I would note that while a very recent conflict with the Kinshaya made the latter's homeworld uninhabitable, it was only one of the more recent conflicts in a long history of war, tension, and almost over-the-top xenophobia. Had the Klingons wanted to make the Kinshaya homeworld uninhabitable before now, they could have. That it took so long to occur suggests to me even in this extreme scenario that planetcracking was not happened. (I wonder what did happen. Accident?)
The Kinshaya became more aggressive, first conquering the Kreel, then making bolder moves against the Klingons. So since the Kinshaya upped their game, the Klingons did as well.
In a twisted way, they were keeping the balance in check. Not an
equal balance of course, but preserving a
status quo. The goal seems to have been to ensure a Kinshaya nation that was at a level of military and political power that couldn't approach an actual threat to the Empire as a whole. It's almost as though the Klingons are
farming reliably antagonistic nations like the Holy Order. The Klingons probably viewed the Kinshaya almost as sport.
"Let's go wander around the Holy Border; why,
what's this, we're being attacked by Kinshaya privateers! Outrage! (Hooray!)*glorious battle ensues, sufficiently challenging but not too overtly threatening*. That was great! Foolish Kinshaya!"
It's like going on tour in Diana Wynne Jones' Fantasyland.
When the Kinshaya became conquerors themselves and incorporated the Kreel, it's like the safari wildlife started massing weapons and marching on the hunting lodge. So the Klingons needed to put the Kinshaya back in their place, and thus they inflict a major blow of the kind they usually refrain from. That achieved, they were happy, I presume.
In
Zero Sum Game, K'mtok moans that the Kinshaya (as well as the Gorn) are using their newfound security offered by membership in the Typhon Pact to boldly harass Klingon holdings. His overall complaint seems very close to "they've gotten uppity on us, I never thought I'd see the day..."