Obama announced last week he would be arming the "moderate" Al Qaeda in Syria, provoking questions of how any part of Al Qaeda can be termed "moderate".
This "ISIS", which has been described as "so hardcore they were kicked out of Al Qaeda" is like a gift for him in that respect. Because now a distinction is being made between "Al Qaeda" and "ISIS hardcore terrorists".
Now, don't ask me why the US would be behind ISIS (and I'm not even convinced they are), but the timely "coincidence" is uncanny and should be factored in when attempting to understand what the hell's going in.
It could well be that these guys have been kicked out of Syria, and told they would not be among the groups to receive arms, and have decided "well, let's do Iraq then". So it could also be blowback in that sense (as they have been supported by the West in Syria so far, and have possibly now gone "splinter/rogue"). But it just seems these guys (ISIS) are so bloody well-armed, that it's actually them who've been directly armed by the US, for some reason. Unless the story is true that they very easily captured the Humvees/choppers etc from the Iraqi army.
The reluctance of the US to make absolutely sure Maliki's government is safe, is quite telling. It's like this is part of a plan. Maliki appealed for US air strikes against ISIS last month, and was turned down. Now, consider how the US is carrying out drone strikes all over the place... Afghanistan/Pakistan/Yemen (killing plenty of innocent people while they're at it). And yet you have this ISIS group rising to power in Iraq, and they don't provide air support? It's all very strange right now.