Thank you all for your responses. (I remember now that STA: Oblivion has early Fed-Cardassian stuff, though I haven't read it yet.) I also think there have been too many wars for my tastes for Trek's utopian future - however I also think that some of those wars produced the best Trek stories (DS9 in particular). For the Federation-Cardassian War, I'm interested in the events surrounding that armed conflict even more than the armed conflict itself. I think of such events, big or small, as part of war - the state of war. (I'm also interested in the events leading up to it.) I think the reason we have so many mentions of war is in part because writers use it as backstory for the episodes they tell - 'Hey let's talk about PTSD and prejudice.' - 'Oh cool - character has issues with a past Romulan conflict?' - 'Nah we've seen them too much - let's make a new species.' - 'Oh ok - we can say the Federation is trying to negotiate peace with them.' - 'Good idea - they can have a border dispute after a war.' - 'We'll call them Cardassians!' Then for those of us obsessed with Trek history, we think 'What? There was this entire war? Who was involved? When did it happen? What was the outcome?' I like Christopher's take: "it had subsided to a cold war by the 2360s, a technical state of declared enmity without fighting (like the Korean War for most of the past 65 years), and that it had never been more than a localized border conflict, to explain why the first two seasons of TNG showed a peacetime Starfleet even though "The Wounded" retroactively claimed there'd been a war going on that whole time." We do have Jean-Luc's line in Chain of Command: " That war cost you hundreds of thousands of lives... depleted your food supplies... left your population weakened and miserable... and yet you risk war again." So obviously the war was a huge cost to the Cardassian Union, but perhaps not as big a deal to the Federation. Maybe those hundreds of thousands of lives were mainly lost due to starvation as Cardassia relocated resources to the war effort - while for the Federation suffered little - excepting a few very bloody border skirmishes (like Setlik III).
"Hundreds of thousands" seems to be lowballing it. That's about equivalent to the annual death rate in America from cancer or heart disease. As wars go, a death toll of hundreds of thousands is kind of mid-sized, something on the scale of the English Civil War or the Crimean War. Even the Korean War had more than a million fatalities, and the World Wars had tens of millions. On the scale of an interstellar civilization with dozens of planets and a population maybe in the hundreds of billions, a death toll of hundreds of thousands does not suggest a very massive war at all.
You’re totally right - I kept reading hundreds of thousands and thinking hundreds of millions for some reason.
I always found Cardassian history interesting. We know some of it from canon, and more from novels. I gather the Cardassian conflict started partly because of their lack of natural resources. I remember in the Terok Nor novels, esp. the first novel about how horrified the Cardassians were at the Bajorans seemingly waste of food (almost as if we invited someone from Sudan to a buffet with us--imagine how horrified they'd be at our waste of food). The Cardassians were still the bad guys, and they commit a lot of atrocities, but it added a layer of complexity that wasn't really covered on screen. And of course in the latest novels they are trying to atone for their history and have come to realize the Federation is not the enemy, but can be a great help. I guess my interest in the Cardassian-Federation conflict is that it's a bit of a hole. It's the one area of Cardassian history we don't know a lot about. There's a lot on Cardassian history out there otherwise (though perhaps there's room for more in early Cardassian history going back to the transition from their Hebition beginnings to Cardassian early history).
There seem to be two conflicting dates for when the Setlik III massacre took place; one just prior to TNG (2362) and another over a decade earlier (c. 2348)