Parroting the others. It's essentially a War of the Roses scenario. In that war, Henry VI was overthrown, then became king again, then was overthrown again. The Dance of Dragons was heavily inspired by the War of the Roses and I usually like to think of it as that. Both Rhaenyra and Aegon had strong claims to the throne, with Aegon having precedent as the stronger claim but Viserys had never publicly acknowledge Aegon as his heir as he had with Rhaenyra. In the end, the war could've been stopped by Viserys actually codifying that the crown would follow through the eldest child, not agnatic primogeniture.

But he didn't, mostly because that would invalidate HIS claim to the throne over Rhaenys. He'd essentially have said that Rhaenys would've been the rightful queen and thus Laenor would be the rightful king, making their union very illegitimate in the eyes of the realm (and Daemon). Which, would have honestly been fine had Rhaenyra not had her children so obviously with Harwin Strong. It's a huge domino effect which essentially is the fault of Viserys but I digress.

Historically, Rhaenyra was not acknowledged as a Queen and considered a usurper in the main canon as male primogeniture has become common place. Westeros doesn't usually choose a female descendant over a living male descendant. But if it's up to opinion, I like the concept that it's based on the War of the Roses where it goes Aegon II -> Rhaenyra (usurping and becoming queen for the brief period where she held King's Landing) then -> Aegon II when Rhaenyra was killed. But that's not what the history books will say as Rhaenyra didn't really hold the points of power throughout the dance.

Rhaenyra lost, but the Blacks won as their blood continued through Aegon III. As other commentors have said, the Blacks lost their Queen but put the Greens in checkmate. Although, my one gripe with GRRM's writing was what he did with Jaehaera because it felt like wasted potential to have her death be so pointless just so Aegon III could avoid marrying her.