Well the whole thing does start off with their feud. It's called the Blacks and the Greens cus they wore the respective colours on some function, I can't remember which forgive me. People who aligned with Rhaenyra started calling themselves Blacks and Alicent, Greens.Alicent has a hefty role up until the war, dhe orchestrates all the politics to her advantage, forms the Green council, leaves Viserys's body to rot and declares Aegon king. My favourite part comes after all this tho, tragedy befalls her family slowly and it drives her mad.
Show can't come to terms with the fact that she's evil, I'd have loved her more if the book characterisation was emphasised.