Além disso, há séculos de inimizade entre o Stormlander e o Dornish, que não iria terminar magicamente. Para não mencionar, os principais aliados de Renly eram os Tyrells, outro dos inimigos tradicionais dos Martells.
GRRM comentou pessoalmente por que Doran não considerou se juntar a Renly:
Q: [Why did Doran not join Renly against the Lannisters?]
GRRM: Doran plays to win, whether at cyvasse or the game of thrones. Likely he did not see Renly as a winner. The emnity[sic] between Dorne and Highgarden also played a part, I am sure.
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Além de
We know that Doran's real end-game is to restore the Targaryens to the throne with his son or daughter as the consort of whoever took the throne.