What Is the Wheel That Aegon Built on Game of Thrones?

The following contains spoilers for Game of Thrones season seven. On Sunday’s Game of Thrones episode, Tyrion and Daenerys have an important conversation about her promise to “break the wheel” that her ancestor Aegon Targaryen built. But what exactly does that mean? The aforementioned wheel is the wheel of power, as in the passing of …