The United States is fighting a war against ISIS. According to The New York Times, the U.S. started to ramp up its attacks on the Islamic State’s finances in November 2015 by going after what U.S. Defense Secretary Ashton Carter called “a critical pillar of the financial infrastructure," oil fields.

The military started bombing ISIS’s oil fields, but in most cases the damage was repaired within days. In this article for The Atlantic, writer Kathy Gilsinan notes that “even if airstrikes can be targeted to do more lasting damage to ISIS’s oil facilities, and the United States can knock out one critical financial pillar, others may be even more difficult to topple.”

Gilsinan then gets into how ISIS is continuing to fund their terrorist activities. While oil is incredibly profitable ($500 million a year!) for ISIS, it's not the group's only source of income: a mix of bank robbery, extortion, and taxation make up a big part of its budget as well. ISIS announced an estimated budget of $2 billion dollars of 2015. (I wasn’t aware ISIS was the type of organization to release budgets, but there you have it.)

ISIS’s finances are like a Hydra; you can take out one but there is always another to take its place. Cam Simpson and Matthew Phillips of Bloomberg Businessweek think ISIS could be bringing in another $200 million a year in crops. They have control of a huge amount of fertile land. Their control of farmlands makes it tough on the US military because, as Simpson and Phillips ask: “how do you conduct airstrikes on farm fields?”

So how do you disrupt the finances of an organization that doesn’t play within the confines of society? ISIS operates a self-contained, largely cash-based economy. They don’t have bank accounts that the U.S. can freeze. They aren’t dependent on large foreign donors, so cracking down on them wouldn’t accomplish much.

Gilsinan says the U.S. and its allies are facing a chicken-or-the-egg type problem. “They may want to choke off ISIS’s finances to help dislodge the group from its territory, but they need to dislodge the group from its territory to choke off its finances," he says.

Bonus info: ISIS has been a big talking point for U.S. presidential candidates. I’m particularly fond of Donald Trump’s plan, perfectly summed up by Tina Nguyen in this Vanity Fair article, “Go to the Internet, where the ISIS is. Close down that Internet, using the brilliant people from Silicon Valley."

That should work.