The low price of oil is a big “natural” weapon to accelerate the defeat of the plague of ISIS.
Oil is by far the main source of their funding: either directly by selling contraband oil produced in the territories occupied by them; and indirectly with the occult financing of some sympathising and oil rich entities.
With the collapse of oil prices, both of these sources of funding become more difficult to obtain and will have a greatly reduced economic impact.
And if the countries fighting ISIS (especially USA, Russia, France and UK) intensify the bombing of oil installations and infrastructures in the territories occupied by ISIS, these fanatical criminals would be defeated in a few months:
NO OIL = NO ISIS
Tankers, that are used in the occupied territories and carry oil to refineries or to the points of contraband sale, should be the first and easy targets. But also refineries, oil extraction systems from wells, pipelines and any oil infrastructure in the occupied territories, must be neutralised. Without the fuel for their own military means, and without revenues from oil that finance heavily their army and all their terrorist activities, ISIS will deflate as a military threat and as a pole of attraction of many desperate and lost souls around the world who are quick to join this criminal folly.
NO OIL = NO ISIS
It is hoped that the low price of oil will last long: it helps fight ISIS, and it is a strong support to the global economy in trouble.
And the world's economies can, not only keep down the price of oil, but also completely eliminate it within a few decades with a determined effort on energy efficiency and renewable sources.
It can be done ... and it is happening, although not quickly enough.