A recent CIA study concluded that arming insurgents has rarely been successful in defeating foreign governments:
The still-classified review, one of several C.I.A. studies commissioned in 2012 and 2013 in the midst of the Obama administration’s protracted debate about whether to wade into the Syrian civil war, concluded that many past attempts by the agency to arm foreign forces covertly had a minimal impact on the long-term outcome of a conflict. They were even less effective, the report found, when the militias fought without any direct American support on the ground.
That isn’t surprising, since this is one of the points that opponents of arming rebels in Syria have made repeatedly over the last three years. To the extent that arming anti-regime forces early on could have “worked” at all, it would have added to the war’s death toll, but probably would not have changed the course of the conflict. This report makes Obama’s decision and Congress’ recent vote to provide arms and training to the “moderate” opposition look even worse than they already did. The administration has known very well for some time that this policy would most likely be useless, but that hasn’t stopped Obama from going along with it to some extent anyway. This suggests that Obama has endorsed a policy that he knows doesn’t make sense and isn’t likely to succeed on its own terms. I suspect that he has done this so that he can throw his hawkish critics a bone in a vain effort to get them to be quiet for a little while. Of course, this doesn’t placate the hawkish critics, and it gives them an excuse to claim vindication that they don’t deserve. Meanwhile, it traps the administration into following through with a policy that no one–including Obama–expects to succeed.