After the failures of Iraq and Afghanistan the US lost its taste for military adventures abroad, apart from the odd drone strike which killed a few tribesmen and their goats. The Arab spring was an abject failure, with only Islamic fundamentalists able to build a cohesive movement to fill the power vacuum. Why this is the case I don't know, why can't these countries build modern democratic movements? And the US doesn't really care about civilians dying anyway, in fact they often back dictators when it suits their interests. Some blame the US and its meddling in the Middle East for Islamic fundamentalism, some blame them more directly for Isis, watch the Adam Curtis documentaries for views on this.