""Do you have any comments regarding US foreign policy over the past 60 years or are you just going to dismiss what you can't refute?"
Plenty. Our withdrawing totally from Iraq is what allowed the Islamic State to cross the border. Our not supporting the secular rebels in Syria in 2011 is what allowed the Islamic State to gain strength initially." Nice to know you can count to 60.
But no, seriously, everything the US does has led to our own detriment. Action? Weakening of enemy government infrastructures so that terrorists can take control and MAJOR fuel for terrorist propaganda. That's why Al Qaeda was so popular in the Middle East after 9/11, that's why the Taliban was popular in Afghanistan and Pakistan during US airstrikes, and that's a reason why some people still join terrorist organizations. Inaction? Terrorist groups can go into the country and have at least a little more straightforward rise to power. It's hard to win.
More relevant to the specific situation: "Sorry Invictus, in this case, the United States *enabled* the existence of ISIS, and now continues to enable their onslaught. We could have dropped troops into Iraq and ALREADY had every last one of those motherfuckers DEAD. Instead, we fly a few airplanes around and say, "Geeeeee....this is gonna take a long, long time..."" Sources say that the video announcing the death of Peter Kassig and showing his severed head were rushed, and that it was likely due to increased drone activity in the area. It showed landmarks, it didn't include the actual beheading (which the aforementioned sources say might have taken place inside), and it was all in one take, as opposed to the others which all likely were over the course of several takes (they give speeches, they obviously can't use several takes to behead someone "Whoops did it wrong, I'll have to try again to get the beheading right. We need to reattach it."). Citizens of the nearby town (because the people beheading Kassig actually gave the name of the town they were near) said there was increased drone activity.
TL;DR
They may be getting scared because of those planes that are flying around that are getting closer and closer to them.