Yes, I'm aware. The Black Dinner was a very small-scale affair that didn't involve an entire army being slaughtered, just two young dukes who the king (being a 10 year old boy at the time) couldn't save - and that dishonor was paid back when many years later, the same now-all-grown-up king personally murdered the son of the greatest magnate who planned it, throwing Scotland into several more decades of unrest.

The Massacre of Glencoe took place centuries after the end of the Middle Ages, when honor had lost its role in politics entirely. The guys who carried it out did so at the command of a Parliament which had just blatantly committed treason by overthrowing their king for another, and then rewrote history to make themselves the unambiguous good guys.

Anyway, my point wasn't that real medieval history was spotless - of course treachery and murder happened - but that it was, relatively speaking, less insanely bloody & backstabby than Westeros' history is made out to be. Even the Byzantines, whose court intrigues have preserved their name as a byword for 'complex and treacherous', would normally balk at pulling a Red Wedding-level affair because it'd destroy their good name; when they actually did (abandoning Emperor Romanos IV at Manzikert, 1071 and the 1182 Massacre of the Latins) it screwed them over massively and greatly hastened the collapse of their empire. Honor was a serious concept in medieval Europe, not the polite suggestion and/or cynical joke of a fairytale that it's treated as in ASOIAF, and regicides were notable precisely because they were actually quite rare; extremely, pointlessly brutal goons like Gregor Clegane, slimeballs like the Freys and the higher lords who enabled them like Tywin typically had short lifespans because of all the enemies they'd make.

I will grant Martin this, though: he does at least try to present some consequences for the Freys & Lannisters post-Red Wedding, even if they were far lighter than what would realistically happen IRL, unlike the show which just wholeheartedly embraces nihilism and doesn't punish anyone for committing atrocities until & unless the plot demands it, ex. Ramsay. By the end there what little message D&D still had basically boiled down to 'believe in nothing and nobody but yourself, betray and murder everyone around you to get ahead, break promises as soon as you make them, always prioritize your own petty squabbles & focus on short-term gratification over long-term thinking - and everything will work out for you'. Which is all well & good if you're a current-year corporate shark but a horrible way to manage a remotely 'realistic' medieval kingdom, to tie this tangent back to what I was saying about how those functioned IRL earlier.