According to this insightful article from the NYT, the earnings from the militants’ violent collection practices total tens of millions of dollars a month, approaching $1 billion a year, according to some estimates.
Source: Predatory Islamic State Wrings Money From Those It Rules – The New York Times
The conclusion is that the only effective way to counter this group is with military force.
Unfortunately, we need to wait for the outcome of the US presidential election to make serious progress.
Thoughts?