When the Islamic State of Iraq and Syria poured out from the eastern deserts of Syria into Iraq’s second-largest city last month, it was an image out of the eighth century: bearded Islamist marauders summarily executing unbelievers, pillaging as they went. But underneath that grisly exterior lurks something more modern and more insidious. As ISIS’s most recent annual report shows, the group is sophisticated, strategic, financially savvy and building structures that could survive for years to come. ISIS currently brings in more than $1 million a day in revenue and is now the richest terrorist group on the planet. Despite the recent calls from hawks in Congress for a broader offensive, there are few meaningful options available to the United States. There’s no political appetite for a ground operation in Iraq. A narrower intervention, like the airstrikes and humanitarian assistance President Obama authorized last week, may be able to limit ISIS expansion, but will not defeat it.