To begin with, the main plot of A Song of Ice and Fire is plucked directly from the English War of the Roses. The war was generations-long and fairly complicated (especially since everyone in English history has one of three names), but it boiled down to a fight for the English throne between the Lancasters (Lannisters) and the Yorks (Starks), complete with boy kings, scheming mothers, a duty-bound "hand of the king," and a royal growing up in far off Europe with a claim to the throne (little Daenerys and her jerk brother).

Before the Targaryens brought their dragons to Fantasy England, they were part of a vast empire over in the Fantasy Mediterranean. Old Valyria bears a striking resemblance to the Roman Empire: both were technically "republics," both empires enslaved people from all across (Fantasy) Europe and the (Fantasy) Middle East, both arose on a peninsula in a warm climate, both built roads and buildings with wildly advanced technology for their time, and both eventually collapsed, leading to centuries of conflict.

In real history, of course, there were a whole mess of different factors that led to the fall of Rome, like invasions and over-reliance on slave labor and too much military spending. But in Martin's world, Valyria just kind of goes up in flames. It's destroyed in a single, natural cataclysm. This volcanic destruction pulls from real world events like the eruption of Mount Vesuvius, which completely buried the ancient Roman city of Pompeii in burning ash. More recently, there was the loss of the Pink and White Terraces, two natural wonders of New Zealand that were buried in the eruption of Mount Tarawera and only just rediscovered.

Yes, the Red Wedding is indeed based on a true story — two true stories, to be exact, and both of them in Scotland. The Massacre of Glencoe went down in 1691, when the clans of Scotland were ordered to put aside the deposed King James VII in favor of King William of Orange. The MacDonalds' signed their oath to William, but the document was delivered late. William's people were not cool with that, so they sent 120 men to the MacDonalds, claiming they needed shelter from the cold. The MacDonalds let them stay, and gave them food and board for two weeks, until one night when the MacDonalds were sleeping, the 120 men murdered 38 of the MacDonald men in their beds, driving another 40 women and children out to die in a blizzard.

The Black Dinner happened earlier, in 1440, when the 16-year-old Earl of Douglas and his little brother were invited to dine with the 10-year-old King James II at Edinburgh Castle. The young king's Chancellor feared that the Black Douglas clan (there was also a Red Douglas clan) was growing too strong, though. So all three kids had a lovely, normal dinner, until one of Chancellor's men dropped a black bull head on the table, to symbolize their house. Then they dragged the Earl of Douglas and his brother outside and beheaded them both (but didn't go so far as to sew the bull head onto the Earl's shoulders).

There was a real wall in the North of England, although it wasn't made of magical ice. Hadrian's Wall was built to mark the northernmost edge of the Roman Empire in Britain, between England and Scotland, and to keep out the wildlings (or rather, the Scots). The wall was also staffed by low-ranking men, forbidden to take wives or have kids.

Wildfire isn't just a magical invention of GRRM. It's based on Greek Fire, a compound used by the Byzantine Greeks in the 7th Century. The exact recipe for Greek Fire is still unknown to this day, but reportedly the substance could ignite on contact with water, destroying enemy ships before they reached land.

In actual English history, William the Conqueror was a bastard Duke of Normandy who wanted to rule over all Seven Kingdoms of England. In 1066, he crossed the (narrow) sea with one hell of an army and started running the place. The current Queen of England is his 22X Great-Granddaughter. In A Song of Ice and Fire, it's the same story, except with Aegon the Conqueror and his sister-wives and their dragons taking over Westeros and establishing the Targaryen Dynasty.

Richard III is a divisive historical figure. On the one hand, he stands accused of murdering his own nephews to secure his spot on the English throne. But on the other hand, there's a good chance that Richard III was actually framed for murdering his nephews, and that in reality he was just a small, witty, slightly hunchbacked guy who was made out to be some kind of monster by his relatives (Tyrion can relate).

Brienne of Tarth is clearly taking some cues from Joan of Arc, minus the whole hearing voices thing. In the 1400s, Joan was a peasant girl who decided that she had been chosen by God to lead France to victory against England. She was a woman with no formal training, but she still managed to lead the French army to momentous military victory against the English at Orléans... until she was captured, tried for witchcraft, and burned at the stake (sorry, Brienne).

Anne Boleyn was the second wife of King Henry VIII, and, like all of his wives, things didn't shake out too well for her. After failing to produce a male heir, she was accused of witchcraft and sleeping with her own brother, George. These claims of queenly incest were probably false... but she was beheaded for them anyway, leaving behind her daughter, Elizabeth I. George was also executed. The Lannisters actually did a way better job at dodging their charges than the Boleyns, even if they were also way more guilty.

The seasons of Westeros are definitely different from the seasons of Earth. But there actually was a Medieval Warm Period, followed by the Little Ice Age, from approximately the 14th century through the mid-19th century. The climate shift wasn't as dramatic as in Martin's fiction, but the drop in temperatures did effect civilization in Europe and the North Atlantic region. Advancing glaciers obliterated farms and churches, and crops failed due to colder, wetter summers, leading to famine. So... the idea of a winter that lasts a generation is really not so fantastical. Martin just added in the zombies.