The Radchaai declared war. Garsedd immediately surrendered, to avoid bloodshed. When the Radchaai troops arrived they broke the surrender and opened fire, destroying several Radchaai warships. Anaander, reportedly quite angry, ordered every living thing in the system killed. It's a bunch of sterile rocks now.

Was this place even a unified polity in the first place?

Yes, split into five regions and twenty-five districts but with a unified government.

Small - well, not mercies, but small things that could have been even worse.

Isabella would like to know when this was, if there were any attempts to preserve the history and cultural output of Garsedd, what became of any Garsedd expatriates who'd left the system before war was declared, and what all the other polities on the map thought about this at the time.

This happened nearly a thousand years ago. The expatriates mostly fled to anywhere that'd take them, and were not reported hunted down unless they were part of the government. There's no reference to attempts to preserve the history and cultural output of Garsedd. 

Other polities were not impressed (nor were the soldiers given the orders; some reportedly mutinied) but, well, a thousand years ago was not a time when anyone contemplated going to war with the Radch.

Does the Radch have the concept of "illegal orders".

Nope they were executed for mutiny.

Isabella writes up an essay-like thing on what she can remember about the implementation of the concept of illegal orders and emails it to Anaander and goes to bed.

That's an interesting implementation. Thank you.

You're welcome.

There are no pacts that encompass everyone, except the nonaggression pacts with the actual aliens (not just the Presger; there's also the isolationist Geck and the Rrrrrr). There are various treaties among non-Radch polities, some of them encompassing as many as twenty. Lots of places have standards for treatment of prisoners, but there isn't a universal treaty for them. The anarchists love free speech! A couple other places value it too. Not as many as you'd expect. Maybe as many as you'd expect if there is actually tons of dangerous information out there.

There is not a specified penalty for reneging on surrender; in the last thousand years no one has tried it, for some reason. 

Anybody tried it before Garsedd?

Nope. Well, there were individual heroic idiots in individual cities or countries but this did not spark systemic retaliation. 

Okay: aliens. What's there to know?

The Geck are aquatic, r-selected, and interact with other worlds through biomechanical mech spiders. At some point humans colonized their planet, and were genetically modified to have gills and be less of a strain on local ecosystems; these humans were considered by the Geck to be peers and friends, but they didn't interact with other humans much at all; the only focus of relations with the Geck has been avoidance.

Less than that is known about the Rrrrrrr. They're less isolationist but there are no humans to serve as intermediaries; Geck-humans are psychologically alien both to Geck and to humans but they're a significant improvement over nothing. The Rrrrrrr are also signatories to a non-aggression pact with the Radch on behalf of humankind. Interestingly, they're currently hosting some Radchaai soldiers who mutinied. They're spacefaring, have colonized at least ten planets and plausibly thousands, and have long salamander-like bodies, furred.

She would like to know more about Geck-humans and about the mutineers - surely the original mutineers are dead, or is this a different mutiny? - and what can she find about Presger?

This is a much more recent mutiny, only a couple of years back. A corrupt system governor was funnelling money into side projects of some kind, and had figured out how to prevent the ship AIs from reporting it. A new ship had jumped into the system, unfamiliar, and the Mercy of Sarse had been sent over to stop and board it. They'd stopped, boarded, realized it was an Rrrrrr ship, and defected. The sympathetic account is that they feared the corrupt system governor, to cover up her corruption, would destroy the ship or kill an Rrrrrr, thus endangering the treaty with the Presger. The less sympathetic account is that the Rrrrrr offered them something. 

Anaander had negotiated the return of the unit leader, and executed her for the mutiny; the Rrrrrr had resisted the extradition for several years, but assented eventually in exchange for assurance that the rest of the defecting unit would be left alone. 

The Presger were the first aliens that anyone encountered. They'd made contact by dismantling ships and their inhabitants, with powers we didn't know anything about or know how to counter. They considered violence against Insignificant species entirely acceptable, and seemed to start from the assumption that other species were; they'd been persuaded eventually that the humans were Significant, and then that the Geck and the Rrrrrr were by the expedient of observing that the latter two could do most things humans could and could be regarded by humans as peers. Intraspecies violence was of no concern to them. Violence between Significant species was abhorrent, except under special circumstances, which no humans understood in the slightest, so everyone was avoiding it altogether. (The Radch had a standing policy that they'd destroy you if you attacked nonhuman Significant aliens, endangering the treaty). 

No one had ever met a Presger. It wasn't clear that they were the kind of thing you could meet. Negotiations happened through translators, humans or human-like people created from the bodies the Presger liked to shred and raised among the Presger in order to enable diplomacy with the humans.

...how many translators are there and where are they? Are there any transcripts of conversations with them? Can she read the transcripts of the trial, if there was one, for the mutineer retrieved from the Rrrrrr? How was the Rrrrrr ship not identified as, at least, a nonhuman ship, don't furry salamanders build differently, can she see pictures - of Rrrrrr, of Geck, of Presger even if they haven't been met perhaps they've been depicted?

There are pictures of Rrrrrr and Geck. There are tons of artistic depictions of Presger; they lean toward the Cubist, and don't otherwise have many features in common with each other. Rrrrrr ships do look different from human ships but ships from different human polities also look different from one another and so it's not definitive that the corrupt governor knew they were ordering people to fire on aliens, though it seems more likely than not. The mutineer's trial was sealed and with Anaander personally; so was that of the governor of Ime Station. 

There are at least ten Presger translators; they tend to arrive unannounced. Everyone just tries to contain and not offend or confuse them.

What offends and confuses them?

It's really unpredictable! That's most of the problem! One of them was deeply bothered to meet a diplomat named Cassav, and demanded repeatedly that she change her name. Small cleaning robots, though not large ones, provoked an intense hours-long series of questions about what they ate and how they reproduced and whether they were prized in society. One of them was once offered a glass of wine and ate the glass. She didn't seem to mind. 

Wow. She kind of wants to meet one but has no angle on that and it would probably be a bad idea anyway.

She studies Radchaai really intensely. She attempts to read baby books in Radchaai. When she manages to read an entire book about baby bunnies of various colors, she (still carrying the tablet, she's not a moron) goes for a walk to explore the neighborhood, wings folded as small as they go.

Toddlers wander through the streets, giggling, their parents strolling behind them. Eccentric hair and eye and skin colors are in, apparently, so she wouldn't stand out much if she cared to do that. She's getting more glances for being white than for being winged but she's not the only white person either. (...she might be the only white person who isn't doing it as a fashion statement). There is a playground and a temple at the end of the street, and a museum across the way.

Everything honestly looks pretty idyllic for being run by a tyrannical mass murderer who seems to be the only person holding together the treaty with some extremely powerful unpredictable aliens.

Yes, well, the United States wasn't all roses either.

She's a little curious about the temple; she loiters slightly outside of it but isn't quite sure enough of herself to go in.

People seem to dress up for it a little bit, and to stay anywhere from ten minutes to an hour. Kids seem welcome, accompanied or not.