What's there to understand? The bulk of Islamic States is an underdeveloped country, where the population is very poor. The only way to make it war or terrorism. It all depends on who and what they will order.
Look at countries such as Qatar, Kuwait and Saudi Arabia. They are among the richest in the world. There are other rich Muslim nations as well, such as Brunei, Maldives, Turkey, and Malaysia. But their behavior is the same everywhere.