#let's give jaehaerys I more credit for absolutely fucking shit up too when he could have just followed regular sexist andal custom on it

[sunderwight]

Thinking about the absolute shitshow that is the Iron Throne and succession on this sunny ash-cloud filled morning.

So as I understand it, there are a lot of different potential inheritance structures for the Iron Throne to be passed down via, because the Targaryens can draw precedents from any of their subjects (Andal, First Men, Ironborn, etc) with varying degrees of viability, plus also Old Valyrian practices, and however they were actually conducting themselves on Dragonstone for the hundred or so years between the Doom and the Conquest. Right? But I think the relevant ones for HOTD are:

Primogeniture, Male Preference vs Absolute Male Preference vs Absolute Primogeniture, Heir Designation, Elective Succession, and Right of Conquest.

Primogeniture is the inheritance model where the eldest child inherits everything. Inheritance isn't divided between potential heirs upon the death of their parent, it's winner takes all. Or rather, eldest son does. This looks to be how most of Westeros operates by default, and how inheritance works according to Andal law. The eldest son (or daughter if there are no sons) gets the title and all the other properties held by his predecessor unless he's been disinherited, and then other successors are determined in a similar order along the family tree (i.e. your next eldest brother would be your heir if you didn't have any kids, then sisters, then first cousins, and so on). But this also applies to heirs themselves, meaning, if you are Jaehaerys I and your son Aemon is your heir, and Aemon's only child and daughter Rhaenys is his heir, then if Aemon dies, Rhaenys gets everything that belonged to Aemon, including Aemon's position as your heir. Which is why Rhaenys would have been the first ruling queen of Westeros, had Andal custom in fact been followed.

Then, male preference and absolute male preference are systems that determine how much sexism is in play when it comes to selecting viable heirs. Absolute male preference means that only men may inherit, and only through their male relatives. Male preference means that sons get preferential treatment, but in absence of them, daughters can inherit (and also that sons can inherit through their female relatives, if applicable). Most of Andal tradition falls under male preference, where an eldest daughter will not inherit before her younger brothers, but it's not absolute because a daughter with no brothers will inherit before her uncles or male cousins. Absolute primogeniture is, on the other hand, when the eldest child is heir regardless of gender. I think this is what Viserys was gunning for, since his negotiations with Corlys and Rhaenys for Laenor and Rhaenyra's children indicated that he expected Rhaenyra's eldest child to inherit the Iron Throne one day, with no stipulation on gender. This would also seem to be the system that Dorne uses.

Heir designation, on the other hand, is when the ruler has the right to personally select their heir from all viable candidates (typically, their children or perhaps grandchildren, or sometimes siblings or even more distant relations). Heir designation doesn't seem to be standard for Andal culture or even what we see of the First Men (hence things like Samwell Tarly being disinherited via the Wall rather than his father just naming his younger brother Dickon as heir over him), but could have been practiced by the Valyrians, and it is this possible precedent of Valyrian tradition which Jaehaerys uses (I think?) to declare his younger son Baelon (Viserys and Daemon's dad) as his heir over his granddaughter Rhaenys, before Baelon's death inspired Jaehaerys to call for the Council of 101 to decide the succession instead.

Which is where elective succession unexpectedly comes into things. I think the only Iron Throne vassal we see practicing such a thing are the Iron Islands, with their kingsmoot? But the Iron Islands are not generally popular or often emulated elsewhere in Westeros, of course, so in this case Old Jae's probably still taking his cues more from Essos or potentially also Old Valyria? The Council of 101 may or may not have been rigged, but at least by appearances, it allowed the lords of Westeros to elect their next leader from a limited pool of candidates (Rhaenys or Viserys).

The final succession structure relevant to HOTD, of course, is the Right of Conquest. Right of Conquest is when the realm will legally grant you the ownership of something if you have seized it via some kind of military might (usually with some stipulation that you have not only taken it, but held onto it for at least X length of time). In Westeros, the Right of Conquest was how Aegon I and his wives used their dragons to establish the Iron Throne, and as a rule it can pretty much overthrow all the other precedents (as it did for the conquerors). But I'm pretty sure this is also why the succession feud after Viserys' death is pretty much guaranteed to become a fight, and it's a major contributing factor to there being so many goddamn civil wars in Westeros. Can't beat your brother's claim? Well, try beating his ass instead!

So... basically, we have a giant, inconsistent mess that has been muddying the waters of the Iron Throne's succession pretty much from the beginning. The Iron Throne follows mostly Andal law and customs, except when the king doesn't want to, and then maybe it follows Valyrian customs or Essosi customs that might be Valyrian or some custom from some other group of subjects or the king just goes "I do what I want" and reminds everyone else (inadvertently, in the case of Viserys) that there is a legal Whoever Punches Hardest Wins clause baked into the system.

Which makes it nigh-on impossible to claim that such-and-such a candidate in HOTD (or even ASOIAF) is being robbed of their rightful inheritance, doesn't it? Whether it's Rhaenyra being the designated heir or Aegon being the eldest son, not just because it's all claptrap anyway, but because there is no stable precedent for who actually has the rightful inheritance even when you're trying to play ball with the existing systems. After Aegon I's death the throne passed to his eldest son, Aenys, but the throne then went to Aenys' brother Maegor instead of his kids. But ultimately Maegor was wildly unpopular and died childless, and so everyone decided that was an outlier and the throne reverted back to Aenys' line, and went to Aenys' son Jaehaerys. Which means there's no firm or stable ground to fall back on before Jaehaerys' own sexist farce of a succession, or the absolute hash Viserys subsequently made of the matter either. Andal law and custom would normally favor Aegon over Rhaenyra, that's true, but those same laws and customs would have also favored Rhaenys over Viserys, and the throne's predominantly Andal vassals voted against that. Which might seem to endorse heir designation, since that was how Jaehaerys selected Baelon and through Baelon, Viserys, as his own successors, but then again the Council was called on the premise that heir designation was insufficient, so perhaps an elective system should actually be in play? But Viserys doubled-down on heir designation and/or absolute primogeniture instead, without even really clarifying which he meant the throne to go by. If he actually filed paperwork beyond the sworn oaths (which he didn't even renew after Aegon's birth or in the decades after), it didn't survive to make into the historical record.

And of course, everything can be upended at any time by a sufficient show of force. Which is not only viable in terms of forcing the issue, but also legally valid, and thus less liable to prompt rebellions and strong rejections from the general populace.

Ultimately we know that the Iron Throne settles on absolute male preference and primogeniture, but all the characters trying to apply this standard to the Dance era are doing so in retroactive judgment.