According to Josh Rogan, of The Daily Beast, http://www.thedailybeast.com/articles/2014/06/14/america-s-allies-are-funding-isis.html, ISIS has been receiving funding from wealthy donors in Kuwait, Qatar and Saudi Arabia, with much of the money coming through Kuwait. This "underbelly" of financial support must be stopped and fully exposed. It is also imperative for the U.S. to determine what role, if any, our oil-based companies have played.
Trying to impose financial sanctions on a terrorist group, is idiotic at best. This ISIS group have become largely self sufficient, they have a large force that is now armed with the American guns left for the Iraqi army. Financial sanction will have no effect what so ever, these people for the time being are past caring about money they have what they need and are taking what they want, which in this case is Iraq.
The only way you are going to stop this group is with troops and with the hesitation of western governments, by the time they finally do deploy troops the situation will have escalated and it will cost a lot of lives to get the situation under control and another long deployment for coalition forces .
No, USA-imposed sanctions will not have any effect on the Iraq situation, because the militants that are taking Iraq over don't see any direct benefit from the aid that the USA provides. They want to take their country back. They are not thinking about long-term implications, or about the strength of the economy.
I have never seen sanctions work as they should. From what I've seen they always make the situation worse and make me think that another solution would have been better than sanctions. Isolating any nation from the world just gives that nations citizens more reason to fight. Starving and/or desperate makes people more dangerous, not less.
If us waging a war there and trying to impose a democracy through military force didn't work then I highly doubt any sanctions the US could impose would do any good at this point. Unfortunately, I feel like there will always be unrest in the Middle East and the best we can do is to help the civilians and protect our own country.