Published by Penguin (I guess that would be Random Penguin now?)
SPOILERS the Kjallans are invading RIGHT NOW RUNNNNNN!!!
There is a really well developed world in these books -- different countries with different climates, ecosystems, cultural mores, languages, but with some shared culture as well (the Cataranga game, the three gods Soldier, Sage and Vagabond, altho Kjall places the Soldier at the top and Mosar has them co-equal, Soulcasting, altho Kjall casts into Riftstones and Mosar casts into familiar animals, etc.). While the primary characters (at least in these two books) are top-of-the-food-chain, Raby puts some effort into showing what the world is like for people further down, and in both books, the protagonists learn more about the scale of their privilege in the course of the story. The values and behavior of the characters in each book are heavily influenced by their culture -- these aren't late 20th/early 21st century imports from our world -- even when the characters begin to see the flaws in their belief system through exposure to another, they cannot simply shed those values. Also, the sex is really well written.
In this outing, Jan-Torres, heir to the Mosar throne and a shroud (invisibility) mage, has sneaked into Kjall to try to find another shroud mage who was spying and sent a message that he had intel that could win the war with Kjall for Mosar, but then never followed up. Turns out (I DID MENTION SPOILERS. OH BY THE WAY, AUGUSTAN IS RIGHT BEHIND YOU.), he's dead. While infiltrating the palace, Janto strikes up a friendship with Rhianne, the niece of the Emperor (I keep hoping that Rhianne eventually gets a chance to track down her mum and her upholsterer dad that she ran off with to Florian's great anger). He helps her improve her Mosar language skills -- she's supposed to move there with Augustan, her betrothed, after Augustan wins the war and gets the governorship. Obvs, Janto would like all of that not to happen.
Little side comment here: I LOVE that Rhianne is comprehensively contemptuous when Augustan attempts to shame her by saying he'll forgive her for the circumstances of her birth. Someone else has to _explain_ to her exactly the game Augustan is playing (which isn't working at all), because it is so foreign to her. She's been abused, but she is utterly confident in her class/status, _which she should be_. If she weren't utterly confident in her class/status, she'd be a clear import. And Augustan _should_ be playing the kind of grind-her-down game that he is, because he's a climber, and he is _not_ at all confident in his class/status. He knows what went into getting to where he is and he correctly figures out Florian's intent in picking him for Rhianne, and knows just how fast he'll be destroyed if he mis-steps at all. Augustan expecting the Imperial Princess to be "more retiring" just shows _how_ out of his depth he really is.
There's a side story about a Mosar slave overseer (male) raping women slaves and how Janto and Rhianne can put a stop to that without killing the overseer. The crux of the book occurs when Augustan returns from Mosar, victorious, and with Janto's parents heads in a box which he pulls out (you know, this is one of the most depressing detached head moments in fiction I've experienced. The Lois McMaster Bujold head rolling down the table, complete with Winterfair gift reference, was easily the best. Same basic idea, really -- I win, you lose -- but it feels so different which side you are on.). This forces Rhianne to expose her feelings; she walks out and life pretty much goes to shit for her. Janto has been exploring the hypocaust that Rhianne helped him escape via, and gets caught so things aren't going to good for him. Lucien (predictably) comes up with a solution that appears to put everything to rights: Rhianne will go willingly with Augustan, Janto will be magicked to forget everything that happened and get dumped on/in Dori, Florian gets the marriage, everyone is happy.
And it almost works. Except Janto fakes that the magick works, and it turns out his brother's fleet is at Dori along with some rebellious Riorcans who took over the Kjallan ships they were on. Bro wants to take the fleet to Mosar, where it will be slaughtered, but Janto knows exactly where all the troops and ships are in Kjall from his spying in the palace (found a report in Lucien's drawer) and has a Much Better Plan.
The moral, of course, is very simple. Florian is Not Nice to anyone (neither, for that matter, is Augustan). Also, Florian is more than a little simple-minded (as, for that matter, is Augustan -- really, a brindlecat kitten as a betrothal gift? So perfect how THAT turned out!). Lucien and Rhianne are basically fair minded people with a lot of power that they try to use to Do the Right Thing, and because Florian is Not Nice (and, basically, simple minded), Florian interferes, enraging them both. Also, Florian preferred the older boys who are dead, so there's historical sibling cray cray. Both Lucien and Rhianne grow up with essentially zero love, affection, etc. to Florian, which, in a succession situation is stupidly dangerous. When Janto, who _is_ trained in diplomacy, shows up, the loyalty to family and state that has been ground into Lucien and Rhianne is not nearly enough to counteract their immediate, deep connection to him, which is based on their shared ethics of the responsibility that comes with power and the importance of compassion and fairness. Even _without_ anyone intending to commit treason, this profound friendship that develops (and the love between Rhianne and Janto) influences several successive decisions. Janto would have been careful to restrain the Mosar when attacking Kjall -- but with Rhianne Kjallan and at risk, he is outrageously careful. Lucien is less influenced by Janto, but once he perceives Janto's ability to maintain what he takes (and that Janto recognizes he cannot himself rule Kjall), Lucien does not make any particular effort to subvert post-battle negotiations (and we totes know he could have!). And Lucien is not at all sad to see Florian exiled prison on Mosar.
In Raby's world, Machiavelli's lessons are turned on their head (I realize this is an oversimplification of Machiavelli). Rhianne and Lucien very much respect and fear Florian, but he does not have their love. And that means that they are just that much more careful and sneaky when they do something they know he wouldn't approve of. Had Rhianne and Lucien loved Florian -- had Florian been even remotely lovable -- Janto would have been dead the second Rhianne figured out he was a spy, or, at the very least, within seconds of Lucien meeting him.
There are more in the series, and more books by Raby. I'm sure I'll get to them. (oooh and author bio stuff says she got her CS degree at UW. If my public records searching found me the right person, I think she probably went through shortly after I did. But see! Another woman who left tech! And _what_ a tragedy that was, her leaving tech to write these lovely books for a major publishing house. <-- a little sarcasm there. Women leaving tech to do something else is NOT a tragedy)