ISIS derives most of its funds from activities inside the territories it now controls, said Daveed Gartenstein-Ross, a senior fellow with the Foundation for Defense of Democracies. That's different from, say, Al Qaeda, which has historically relied on donations from outside sources.


"When they control a territory that's approximately the size of Great Britain, that creates a great deal of ability to get internal sources of revenue, ranging from natural resources, to antiquities they control, to taxation on their population," he said.


Pic: Islamic State militants blew up the Arch of Triumph, a historic monument in the 2,000-year-old Roman city of Palmyra in Syria. Sale of antiquities from sites it loots funds the group.