It's a piece of fiction, and not even historical fiction (like, for example, Philippa Gregory's Tudor Court novels or Colleen McCullough's Masters of Rome novels). It's a fantasy series. Why would it be accurate? What should we compare it against?
I would say it's an extremely inaccurate depiction of the early days of Australia. It's also inaccurate at depicting the Imperial Court of China.
Against what would we measure its accuracy, given that it's a piece of fiction in the fantasy genre?
A better question might be: "what historical allusions can one identify in ASOIF?", but that's probably not a question for this sub. As noted by the others, these questions, as they are, are pretty much unanswerable because there's nothing to use as a baseline for comparison.
No story spoilers past AGoT, for those concerned about such things.
Aspects of the books do parallel events in history, though more by resemblance than exact correspondence. In no particular order:
The feuding between House Stark and House Lannister is broadly reminiscent of the British War of the Roses between House York and House Lancaster.
The settling of Westeros, with the pagan First Men followed by the Andals with their organized religion is like the settling of the British Isles, more or less. The clincher - the entrance of a new king from a new land who speaks a new language who conquers the settled peoples. Aegon the Conqueror is William the Conqueror, but with dragons.
Warfare is a bit off. Far too many pitched battles and not enough sieges. Sieges were far and away more common than all-out assaults. Also not enough polearms: swords were the equivalent of pistols for most foot soldiers, if they were using them and not their polearm (rifle), something had gone wrong. And people need to wear their goddamned helmets.
Castles in ASoIaF are more formidable than real-world counterparts, perhaps because the armies of Westeros don't go in for heavy siege trebuchets the way they should. Heavy trebuchets could and did end sieges with just a handful of throws (once built, of course). In an extreme case, Warwolf, built at the order of King Edward Longshanks to attack Stirling Castle, led to the surrender of the garrison before it even fired once. Edward refused to accept the surrender until he'd gotten his money's worth and leveled a large section of wall.
The Free Cities of Essos are a sort of amalgam of Renaissance Italian city-states, classical Greek city-states, and Muslim cities in Spain and Turkey.
Slaver's Bay is weirder - Rome at her height mixed with Medieval Egyptian slavery practices, particularly the Mamluks.
The faith of the Red Priests is heavily drawn from Zoroastrianism, with its featuring of fire in worship and emphasis on a single all-powerful deity locked in struggle with a great evil power.
So, not bad, but not plausible down to the nuts and bolts.
hi! there have been lots of questions in this sub about various aspects of the tv/book series; a few have been collected in the FAQ* - check it out for previous responses
*see the link on the sidebar or the wiki tab