A detailed WaPo article, with many links, that looks back to the early days of the Syrian Civil War 'Would arming Syria’s rebels have stopped the Islamic State?':http://www.washingtonpost.com/blogs/...islamic-state/

It starts with:
Former secretary of state Hillary Rodham Clinton made news this weekend by suggesting that the rise of the Islamic State might have been prevented had the Obama administration moved to more aggressively arm Syrian rebels in 2012. Variants of this narrative have been repeated so often by so many different people in so many venues that it’s easy to forget how implausible this policy option really was.

(And ends with) Had the plan to arm Syria’s rebels been adopted back in 2012, the most likely scenario is that the war would still be raging and look much as it does today, except that the United States would be far more intimately and deeply involved. That’s a prospect that Clinton frankly acknowledged during her interview, but that somehow didn’t make it into the headline. As catastrophic as Syria’s war has been, and as alarming as the Islamic State has become, there has never been a plausible case to be made that more U.S. arms for Syrian rebels would have meaningfully altered their path.