While not condoning anything IS does, how about considering the US involvement in all the worlds problems.
7 of the top 10 arms manufacturers are American, see here:
http://www.sipri.org/research/armaments/production/Top100.
The US has been involved in almost all the military conflicts all over the world since the second world war, including fighting in Korea and Vietnam and other countries, but also funding many military groups (including terrorist groups) and dictators.
It has removed leaders from some countries (sometimes by killing them), particularly those in South America. Here is one example:
http://en.wikipedia.org/wiki/Operation_Condor
It used AWFUL things in Vietnam including Agent Orange and Napalm. It is estimated Agent Orange alone has resulted in about 3 million people in Vietnam being affected by Agent Orange, and many children being born with defects.
http://en.wikipedia.org/wiki/Agent_Orange
http://en.wikipedia.org/wiki/Napalm
You have to remember that the USA got very rich during WW2, by making and selling military equipment to the UK and other countries. After the war many business people in the USA decided that this was a good way to make money and stay rich.
Eisenhower, who led the D Day landings in WW2, became president after the war, and in his Presidential resignation speech he made reference to the Military Industrial Complex and how concerned he was about it (and this was from a military man).
http://en.wikipedia.org/wiki/Military%E2%80%93industrial_complex
While we should not condone what IS are doing and who funds them, we have to see this as a world wide problem of some countries (US and Russia for example and even the UK) supplying military equipment to both sides in small local conflicts.
If you look at most of the "small conflicts" since WW2 it has mainly been where the USA are supplying arms to one side, and Russia supplying arms to the other.
Sometimes I do feel that e USA pokes its nose into conflicts where really it has no right to do so.
So while IS is a problem, the military might of the USA and Russia is probably a larger problem.