An internal succession war within House Targaryen at the height of its power, 172 years before the birth of Daenerys Targaryen.

The Targaryen dynasty is at the absolute apex of its power, with more than 10 dragons under their yoke. Most empires crumble from such heights. In the case of the Targaryens, their slow fall begins when King Viserys breaks with a century of tradition by naming his daughter Rhaenyra heir to the Iron Throne. But when Viserys later fathers a son, the court is shocked when Rhaenyra retains her status as his heir, and seeds of division sow friction across the realm.—Canon y mus

Nearly two hundred years before Game of Thrones King Viserys of the House of Targaryen is the undisputed ruler of Westeros and surrounding lands. However, when he names his daughter Rhaenyra as his heir he sets in motion a series of events that many years in the future will lead to a bitter feud over who should sit on the Iron Throne.—grantss