Back before the dragons, the Lannisters had more than enough cash to sponsor a fleet to invade and eradicate the Ironborn from the Iron Islands.
One among many of the dumbest & silliest parts of the lorebooks about shit that happened centuries/millennia before Aegon's Conquest was that this exact thing
HAD happened already. The rundown is that the Hoares once produced three miraculously non-turbonigger kings in a row, all named Harmund, who tried to curb the most violently retarded and pestilential aspects of Ironborn culture (they promoted trade & peaceful relations abroad, discouraged reaving and slaving, were not rabidly anti-intellectual and eventually tried to convert the Ironborn away from the Drowned God to the Seven). Naturally,
the third & last of them was overthrown, mutilated and tortured almost to death by the Ironniggers, who really want to keep their barbaric crab bucket going. They also mutilated his mother...a Lannister princess, and aunt of the King of the Rock at the time, to whom she was sent back minus most of her facial features.
So the Lannisters invaded the Iron Isles in retaliation, and actually won! They butcher
the last good Iron King Harmund's brother, who betrayed him & their mother to the Ironborn fanatics, and occupy the Iron Isles. At this point they have the Ironborn 99% buckbroken and pretty much totally at their mercy, or lack thereof. But then
their general goes rogue, declares himself the new King of the Iron Isles, and in response...the Lannisters don't just fire & replace him but instead pull out of the Iron Isles altogether. This Crakehall character obviously couldn't have had much support among the Westerman soldiery, because the vast majority of the army followed the Lannister king's orders and left him to get drowned by the Ironborn. Adding further insult to injury, they didn't even kill the guy responsible for starting the anti-sanity rebellion and torturing both Harmund & Lelia Lannister before, this
'Shrike' survives to be the one to drown Crakehall. The Ironborn pretty much get away with this atrocity as they did many others which should realistically have been kingdom-enders, they recover later and in fact the peak of their power comes centuries after this debacle.
Meanwhile IRL, in response to the butchering of his envoys by the Shah of Khwarezm & his governors, Genghis Khan famously killed 90% of the Iranian population in his vengeful rampage and turbofucked that region so hard it wouldn't reach the pre-Mongol population level again until the fucking 20th century. Imagine how much harsher he would have been if they'd mutilated & tortured his sister, his aunt, his niece or his daughter instead! Not even the bugs & other vermin would've been allowed to live when he was done with the place. And the same is true of pretty much every other famous king from the Middle Ages, even the nicest and most humane among them couldn't have allowed the sort of shit the Shrike pulled go, if not because they really wanted to avenge their kinswoman then at least because it'd make them look cripplingly weak.
Even if we were to entertain the argument that maybe a Ned-like King in the North or the Gardeners of the Reach (who have a reputation as generally kindly, benign & diplomatic rulers) might have gone easier on the Ironborn, which they probably wouldn't have because of what I just said above, the Ironborn pulled this shit on the Lannisters no less - a house with a historical reputation for being pretty damn cutthroat. (The fact that the Lannister king at the time invaded the Iron Isles in the first place also already goes to show he wasn't a pussy that could've just been walked over like Tytos, Tywin's dad.) Tywin destroyed the Reynes & Tarbecks, and also plotted the Red Wedding, for waaaaay less than what the ancient Hoares & Drowned Priests had done. This bit of lore and the lack of a 'Rains of the Iron Isles' song from centuries or millennia before the Conquest, like the Boltons still being around, is a fantastic example of how there absolutely is plot armor in Gurm's works, it's just mostly worn by the villains (whether individuals or entire houses/cultures).
It's ironic. The Andals and their Faith of the Seven are the only people without magic powers or liberal reforms. The First Men in the North have their old gods, the Targs and Valyrians have dragons, blood magic, and the red god, the Dornish Rhoynar are more sexually free and respectful of women, the Ironborn captains vote for their king, it's the Andals and their pseudo-Catholic Faith of the Seven who are the picture of regressive, patriarchal, religious feudalism, and yet they're the most functional. They're everything Martin hates about the Medieval world, and he constantly bitches about their way of life, yet he accidentally made them the most stable.
They're not sexual degenerates like the Dornish, they're not brutes worshiping a Weirwood hive mind like the Northerners, they're not incestuous blood-magickers like the Valyrians, nor do they practice human sacrifice like the disciples of the red god do. They also don't steal damn near everything like the Ironborn. They maintain several kingdoms in the warmer, more prosperous part of Westeros, and despite some wars between these kingdoms, they had a distinct balance of power that kept them all in check before the Targaryens showed up. And even the Targs adopted their religions and customs to fit in, knowing that it's more stable and orderly than what the North, the Ironborn, or the Dornish were doing.
The FO7 gets a ton of shit from fans for being the only religion without obvious superpowers - and thus, undeniable proof that their God or gods are real - in the setting, but maybe we've been looking at it all wrong. Maybe the Faith's true superpower, in fact, is in the
friends stable & functioning societies it made along the way (of thousands of years), and unlike the rest it doesn't need boatloads of human sacrifices to deliver that result.
A running theme in Martin's work is that the smallfolk are basically apolitical normies who just want to grill, and give infinitely less of a shit about the intrigues of their overlords or weird ass magic tricks than they do about living to see another peaceful sunrise with their friends & family, exemplified with quotes like this (from Jorah to Dany):
The common people pray for rain, healthy children, and a summer that never ends. It is no matter to them if the high lords play their game of thrones, so long as they are left in peace. They never are.
Well, for all the flashier powers of the other religions on Planetos, the Faith's the only one that can even come close to granting that wish of the masses, and so what it has to offer is valuable in its own way. 'Not all that is gold glitters,' etc.