Before the Battle of the Blackwater, why did the Tyrells need to meet up with the Lannister host? I was thinking it was to finalize the marriage deal between Joffrey and Margery, but even knowing that Tywin’s the one who really calls the shots, it’s not like they need his approval at all before hand. Couldn’t the Tyrells have accepted the deal from LF and just attacked Stannis with their own host, w/out Tywin, like if he had crossed the Red Fork or Arya had named him as one of her 3 kills?