How Long Can the Islamic State Stay in Business?

The richest terrorist group in history is financed not just by smuggling oil and selling looted antiquities. It may get as much as a billion dollars a year from taxation on individuals and businesses subject to a system of brutal enforcement. While increased bombing may deplete oil revenues, beatings and even beheadings are taking a toll on formerly middle class people. We hear about a model of governance that could threaten the sustainability of the Islamic State from the inside.