A similar idea to this was address in the last @girlsgonecanon episode in which they mention the status the Targaryen build for themselves. I wanted to explain properly this tweet that I made. https://twitter.com/Argsoiaf_/status/1344907319386255360

Early Targaryen committed incest to maintain the bloodline “pure” and be able to continue riding dragons. Despite I'm against incest this created the idea that Targaryens were some type of demigods, superior to the rest of people, and that they were the only ones that could rule

This was possible because they have dragons and they extended the doctrine of Exceptionalism using the Faith, avoiding the image of the abomination they had at the beginning.

After the Dance of the Dragons Targaryens lost what allows them to be a superior family, so slowly they started to marry into westerosi families (something that has been done before, but on a smaller scale). Losing the image of being a House above the rest of the nobles.

They look to replace this with carefully crafted alliances with the greatest families (actually a clever idea by them). Due to several reasons, these alliances weren’t completed, and they only united with relatively small Houses compared to their early plans.

Then they went back to committing incest, for love and some dubious prophecy, but they now lack the Dragons to justify it. They were no longer Demi-gods that were chosen by the Gods to rule Westeros, as the Dragons suggested.

Now they were another normal family and incest was again an abomination. All this slowly planted the idea that they could be replaced by other Westerosi House with better alliances and only some Targ blood.

I am not saying that this is the one and only cause of Robert’s Rebellion, but that it implanted the idea among the nobles and smallfolk that they could be replaced.

I think that early Targ incest was relatively justified (not really) and that trying to build alliances throw marriage was intelligent, but they ended not doing one or the other and this midpoint contributed to their downfall.
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