The Islamic State, or ISIS, has proven to be persistently successful in attracting people from all over the globe to join in its state-building and state-defending enterprise. This article explores the messages it has crafted, from the utopian to the militarily defensive, and the techniques it uses to propagate these messages (including on social media), which includes some historical comparisons to communism and Nazism. It goes on to provide initial research findings from the field to show how their message is working among (a small percentage of) the target audience, sketching the theory of identity fusion to argue that it is a sense of belonging to one group above all others that persuades people to travel to another country to kill and die for a cause.