Going by Brian's posts, it is interesting to note that originally ASoIaF was a trilogy consisting of A Game of Thrones, A Dance with Dragons and The Winds of Winter. AGoT originally ended with the Red Wedding and was primarily the story of the War of the Five Kings. ADWD picked up five years later and mainly focused on Daenerys, events in the East and her return to Westeros. TWoW focused on the North, the Others and Jon Snow. All three stories intermingled in each book (Cersei's descent into madness, her arrest, the rise of the Faith etc was also planned for the very original conception of ADWD), but that was the focus in each one.
.