Imperialism Wow!
(To be pronounced, naturally, just like "Catholicism Wow!". You may feel free to imagine for yourself Buddy Queen Victoria, Buddy Cecil Rhodes, Buddy Genghis Khan, or Buddy Gaius Julius Caesar Augustus.)
In which I write in response to this comment back on "Nom":
Are there any circumstances where the Empire of the Star would involuntarily annexe a place or a people? Or would they just burn it instead, if walking away and leaving it alone was inadvisable?
(Of course, arguably, the Empire never needs to annex anywhere because of the Doctrine of the Ecumenical Throne, which in a manner entirely familiar to classical China holds that the Imperial Couple already rules everything under Heaven and it's just that some benighted places don't realize it yet.
Well, okay, technically the Imperial version holds simply that as the only government whose mandate is legitimate - which is to say, in accordance with the Fundamental Contract - their Divine Majesties’ authority is accordingly universal, and that the countless polities in existence differ from one another only in their degree of integration to the Empire, the degree of their compliance with the Imperial Mandate, and the manner in which the Throne’s authority manifests itself.
...this particular doctrine has been largely held in abeyance at least since the unification of Eliéra, and tends to be brought out only under special circumstances, but it's never been formally repudiated, either. It's so useful!)
But that aside aside, let's narrow the scope a little, and presume we are talking about the modern Empire. (Obviously such things were done earlier in history, or people wouldn't be concerned with the Imperial diet, after all.)
Yes.
Not preemptively (for reasons as summed up by Rens Houben here), although I do note that those qualifications apply to the preemptive, "do you have a flag?" style of conquest. That's out of fashion. As a smart and stylish Hegemonic Empire, they greatly prefer seducing people into wanting to join up.
But that does not exclude the many cases in which someone is, say, unwise enough to directly or indirectly pick a fight with them¹, in which case, as Brennus the Gaul said, vae victis.
Not all that much vae, though. The thing you have to remember is that by and large, this is the good outcome. And it's one reserved for those worthy opponents who are both appealing to the Imperial diet and (to invoke a variant of this) can be conceived of as making a mistake.
To make a historical analogy², imagine the Empire in the position of the US in the Pacific theater of WWII. From their point of view, they can conceptualize Imperial Japan, historically another member of the advanced (and meteorically advancing), civilized nation club, as a polity that have been led down a path that is horribly, horribly mistaken.
But they can see the good bones underneath and what they could be (i.e., something closer to the modern nation), were it not for the fascist lunacy currently in charge.
The win condition, therefore, for the hypothetical Warmain of the West, isn't to destroy the enemy. It's to defeat them, certainly, and force an unconditional surrender, but in the long game what they have in mind is that they can fix them. In this scenario, the occupation takes the form of satrapy-as-prelude-to-annexation, in which - while the war crimes trials are likely to be rather harsher than in actual history - there is a focused and serious effort dedicated to reform and recovery (with incredible generosity) designed to get the satrapy to the point where they'd willingly, if not entirely voluntarily, accept annexation as a peer Imperial constituent nation.
Like the proverb says, "We best destroy our enemies when we make them our friends."
This, of course, is the ideal outcome. Such outcomes are not available to those places that don't suit the Imperial diet, for obvious reasons (if they don't think you'd be a potentially good fit when you weren't on the other side of a war, they're not going to change their mind on that when you are); your best outcome there is one of the other kinds of satrapy, the ones imposed by a stern peace treaty and designed to keep an eye on you and make sure you don't cause any more trouble.
They're also not available to those where it isn't mistake, it's conflict, in the sense that your fundamental goals as a civilization are completely incompatible. If you're heavily into, say, slavery, or communism (but I repeat myself), or oppressing the hell out of people, or killing all the Space Jews, or some such, then your menu of options starts with a generous round of rock storming and goes downhill from there. You can't negotiate with cancer, because it will take your favorable terms and murder you with them.
And what of the other Presidium powers?
It varies. The Echelons, maybe, if adequately provoked, but they're more likely to sign you up as a client-state or military protectorate.
As for the others, the League of Meridian doesn't have the patience for it, although it can be sucked into peacekeeping alongside the Echelons; the Photonic Network are completely uninterested in governing meat close-up; and the Under-Blue-Star League³ are too cryptic to make definitive statements about.
- It has turned out more than a few times in history that being likeable by Imperial terms is a very sound defense policy, much like being "Friends of the Senate and People of Rome". For values of turned out equal to someone who thought they were bullying their weak and defenseless neighbor, only to look up and discovered they just punched God in the face.
- And, yes, there are plenty of historical details that can be quibbled with, here. It's an analogy. Run with it.
- The voctonari, while little-appearing, are weird to the point that basically it's like having the Vorlons on the Presidium. You ask them for a definitive statement on any given instance, you're more likely to get "Annexation is a well-aged cheese served at room temperature." than anything you can actually comprehend.