From The Economist:

Earlier this summer two dozen American commandos swooped into northern Syria in an effort to save James Foley, an American journalist (pictured), and others being held by the Islamic State (IS), an al-Qaeda-inspired jihadist group. The soldiers raided an oil refinery controlled by the militants, but found no hostages—they had been moved. The daring rescue attempt shows the lengths to which America will go to save the lives of its citizens. But Foley’s ultimate fate shows the limits. When his captors demanded a multi-million-dollar ransom in return for his release, the American government declined. On August 19th IS put out a video showing one of its members beheading the journalist. America is obviously concerned about the safety of its citizens abroad, so why does it refuse to pay ransoms that might save their lives?