They had asked if he would lead the attack, offering him a position of command. Would he never be more than their errand boy, sent to do their grunt work so their ridiculous robes wouldn't be soiled by the breath of other species? "Renegades, for all the Capitol's disdain, were really useful beings in the end, weren't they?"
The Capitol needed him again. He didn't need them, but he was the Doctor. They were the Daleks. His mortal enemies. It was no use trying to guess who started it. But the Council offered him this chance to end it. Forever.