What was the Dance of the Dragons?

Why did the war begin?

Because a king tried to change the rules of succession and then made it impossible for his choice to stick. Viserys I named his daughter Rhaenyra as his heir, which no Targaryen king had done for a daughter. He then married again and had sons, and a king's son gave everyone who doubted a queen regnant a candidate to rally around. Viserys made his choice, but he never made it safe.

That left a court divided for years before any blood was shed. One faction gathered around Rhaenyra as the heir the king had named; the other around his second queen and her sons, with the weight of tradition on their side. When Viserys died, each faction could argue in good faith that it was defending the law, and each had dragons. That combination, rather than any single villain, is what made the Dance so destructive.

Who were the Blacks and the Greens?

The names come from the colours each side used. The Blacks stood for Rhaenyra and her claim, with her husband Daemon Targaryen as their leading commander in the field; it was Daemon who led the Blacks in taking the great castle of Harrenhal. The Greens stood for Aegon II, Rhaenyra's half-brother, and for his mother's side of the court.

What makes the war hard to follow is that the two sides were not two houses but one family split down the middle, with the great houses of the realm choosing sides around it. Uncles fought nephews, a half-sister fought a half-brother, and children on both sides became targets. For readers, the colours are the only quick way to keep the allegiances straight, which is why both the book and the series lean on them.

Why were the dragons the real casualties?

In earlier Targaryen wars the dragons were the family's unanswerable weapon. In the Dance they faced each other, and a dragon killed by another dragon could not be replaced. Battles like the ambush at Rook's Rest, where Sunfyre and Vhagar together fell on the dragon Meleys, show the new arithmetic: every victory cost the family a piece of the power that had made it the ruling house in the first place.

By the end, so many dragons had died that the Targaryen dragons never recovered, and the war is remembered as the beginning of their extinction in Westeros. That is the deepest irony of the Dance. Both sides fought for a throne whose authority rested on the dragons, and between them they destroyed what the authority rested on. The Targaryens kept the crown for more than a century afterward, but without the beasts that won it.

How do we know what happened, and how much should we trust it?

Everything known about the Dance comes from histories written inside the world, and they disagree. The fullest account is Fire & Blood, from 2018, presented as the work of an archmaester who weighs earlier chroniclers against each other and often cannot say which is right. A shorter version of the same events appeared first as The Princess and the Queen in 2013.

That framing is a gift to adaptation and a caution to readers. Where the sources conflict, House of the Dragon is free to choose one version or invent its own, and it does both. So the best answer to any detailed question about the Dance usually comes in two parts: what the history reports, with its uncertainty, and what the series chose to show. The page on the show and the book takes up the differences.