The game of brinkmanship being played out in Syria could affect us all

For well over a year ISIS seem to have been able to act with impunity, selling oil to finance their war, fighting with the kind of hardware that Al Qaeda could only dream of, taking city after city; all while the US seemed ‘unable’ to stop their progress or intervene.
ISIS were being ‘sold’ to us as monsters worse even than Al Qaeda, so why was no-one willing to do anything effective?