The Targaryen civil war known as the Dance of the Dragons will play out in House of the Dragon, HBO's first Game of Thrones spinoff, and that could end up connecting to The Winds of Winter. While Game of Thrones ended in 2019, there's still a lot more of Westeros' story to be told. That's true on the screen, with many other Game of Thrones spinoffs planned for after House of the Dragon, but also on the page too, with George R.R. Martin still writing The Winds of Winter, the sixth and penultimate book in the A Song of Ice and Fire series.
House of the Dragon begins around 200 years before Game of Thrones (and so The Winds of Winter as well), telling the story of House Targaryen being divided by claimants to the Iron Throne after the death of King Viserys I Targaryen (though the seeds are planted much earlier). That results in the Dance of the Dragons, a civil war that splits the realm in two, separating into supports of the "greens" and the "blacks," the warring Targaryen factions behind either the claim of Aegon Targaryen or his half-sister Rhaenyra. The name of the civil war refers not only to the rivalry, but just how much of the war is fought with dragons.
Rather than just being its own isolated story, this could also inform what is in The Winds of Winter and/or Martin's final A Song of Ice and Fire book, A Dream of Spring. The events of the Dance of the Dragons are already written, of course, but this could be a case where history repeats itself (a theme Martin is extremely fond of). With House of the Dragon showing The Dance of the Dragons, it's possible The Winds of Winter will actually include its sequel, a fiery clash between two Targaryens who both believe themselves the rightful ruler of Westeros.
Daenerys vs. Aegon? Winds Of Winter Could Have (or Set Up) The Dance of the Dragons 2
A key book character missing from Game of Thrones was Young Griff, who is revealed in A Dance with Dragons to be Aegon Targaryen, the long-thought-dead son of Rhaegar Targaryen and Elia Martell. Though there remains a lot of reason to doubt Young Griff is truly Aegon, it may not matter too much for where he is headed in The Winds of Winter's story. Aegon has already arrived in Westeros, and has his eyes set on the Iron Throne. There's reason to believe it too. Partly this comes from prophecies: Daenerys is warned of a "mummer's dragon," which is believed to refer to Aegon and how he is being used by Varys and Illyrio Mopatis; she also sees a "cloth dragon on poles" amid a cheering crowd, suggesting Aegon will be beloved. But it also fits his arc: he has been raised as the perfect prince, and will be arriving in Westeros as the miraculously alive son of another beloved prince, Rhaegar. He will have the Golden Company, the greatest army of sellswords available, behind him, and like several major Westeros houses as well (Dorne is already shaping to pledge its support to him).
All of this positions Aegon to become King, and crucially do so before Daenerys has even set foot in Westeros. That's important, because it means Dany is finally going to come to Westeros to claim the Iron Throne she believes is hers, and discover another Targaryen already sitting on it. Dany has already been on a dark path to take what is hers with fire and blood, so the presence of Aegon likely isn't going to go down too well with her, though he himself may try to offer marriage (something she would surely reject). That, then, would mean war: Daenerys vs. Aegon at the end of The Winds of Winter (or set up for the beginning of A Dream of Spring) would be the Dance of the Dragons 2.0, another Targaryen civil war to divide Westeros, and one that could see dragon vs. dragon.
As it stands, Aegon doesn't currently have a dragon, but there are ways he could get one: Dany might ask him to ride one to prove his Targaryen family heritage; he could be able to bond with and steal one; there is the magical dragon horn in play, said to bind a dragon it its user, which could end up being a factor somehow. It's quite possible that Aegon ends up riding Rhaegal, the dragon named after his (apparent) father; this would even mean a repeat of the greens vs. the blacks, with Aegon on the green dragon and Daenerys on the black Drogon. This could even be how Daenerys destroys King's Landing in the books; not a deliberate act of a would-be Queen on a vengeful rampage, but as collateral damage of a battle between dragons, whose fire causes chaos and ignites the stores of wildfire under King's Landing.
Even with all of The Winds of Winter's other questions to answer and storylines to resolve, Daenerys and Aegon should be a major factor, and the Dance of the Dragons seems the most likely way to resolve it. The Winds of Winter's preview chapters have already hinted at it, with Arianne I including the lines: "They were dancing. In my dream. And everywhere the dragons danced the people died." As if that's not enough, in a 2003 interview [via Westeros.org], Martin himself responded to a question about learning more of the Dance of the Dragons by saying: "The first dance or the second? The second will be the subject of a book. The first will be mentioned from time to time, I'm sure." Plans may change, of course, and there are other possibilities, but it does seem that, like with House of the Dragon fully showing the Dance of the Dragons (which Martin did more than mention, writing in depth about it in Fire & Blood), then The Winds of Winter will have or set up the second.
How Winds Of Winter's Dance Of The Dragons Will Be Different To House Of The Dragon's
The Winds of Winter's battle between Daenerys and Aegon will likely be rather different to House of the Dragon's civil war, for a few different reasons. Part of that is simply the state of House Targaryen: in the latter, it's at its peak, allowing for different factions and rivalries that build up over decades before the war even begins; in the former, there are only two Targaryens (assuming all of this comes well before Jon Snow's parentage is revealed). The first Dance of the Dragons took place across several key Westeros locations, involving all major houses, and lasted two years; the second will likely have a massive impact, but could be rather more contained to King's Landing, which will likely suffer the brunt of the conflict. And, of course, there aren't as many dragons either.
There will be 17 dragons in House of the Dragon, whereas The Winds of Winter will likely just have Daenerys' three dragons, albeit with one changing sides, unless Aegon is able to discover another dragon (which, again, is possible with magic artifacts in play - blowing dragonbinder could stir other dragons; there are some from the Dance, such as the (mostly) wild Sheepstealer, whose fates are unknown, so it's possible other dragons are still alive in Game of Thrones' world). Still, for all its differences, there will be thematic parallels between the two versions of the Dance of the Dragons, with each allowing Martin to provide his commentary on the true horrors of war, of the dangers of wielding such weapons and the responsibility of that power, of how those who seek to rule are often least suited to doing so, and of how when the nobles war, it's the smallfolk who pay the heaviest price.
Why Did Game Of Thrones Cut Aegon Targaryen?
If The Winds of Winter does lead to Daenerys fighting Aegon, then it also again leads to questioning just where he was in Game of Thrones. It would have been impossible, of course, for the show to have adapted everything from Martin's A Song of Ice and Fire books, and Young Griff in particular is a late-in-the-day twist that's tricky to incorporate, especially on TV. It would've had to come during Game of Thrones season 5, by which point the show was already moving away from the books - with The Winds of Winter still unfinished - and impacted its line to the endgame. With Game of Thrones also having to reveal Jon Snow is a Targaryen at some point, then unveiling another secret Targaryen - and to then potentially reveal he's a fake later on - may have been overkill for more general TV audiences. With all of that, then it makes sense Game of Thrones cut the Aegon Targaryen twist, keeping its focus on the characters it did have already, and allowing some greater surprises to come in The Winds of Winter.