Nikolas Gvosdev lists the possible consequences of providing arms to insurgents in Syria. He points out that there is no way of knowing how these weapons will be used:

Indeed, America’s 1980s experiences with supplying arms to the mujahedeen in Afghanistan and the contras in Nicaragua highlight some of the problems with weapons transfers. Groups on the ground may want to horde weapons for use in internecine battles with rivals to establish their dominance after the enemy has been defeated. Gulbuddin Hekmatyar, the Afghan commander who received the lion’s share of military aid from the U.S., Pakistan and Saudi Arabia during the fight against the Soviets, was notorious for his attacks against rival mujahedeen groups, especially those led by Ahmad Shah Massoud. Some of the weapons he received from the West were used, not to drive out the Soviets, but to turn parts of Kabul into smoking rubble during the 1990s when he attempted to take power for himself.

One would think that America’s largely uninspiring record of arming insurgencies in the past would eliminate any desire to try again. Something that continues to impress me about interventionist arguments on Syria is how very short-sighted they are. Most Syria hawks are not concerned with who will govern Syria or how in two or five years’ time, but are preoccupied entirely with finding some way to get the U.S. into the conflict regardless of the effects that this could have in and around Syria. If an even worse government came to power through U.S. and Western military aid, or if these weapons helped fuel another decade of civil war, the U.S. would be partly responsible for condemning Syria to even more suffering, and worst of all our government would be doing this for no good reason.

Gvosdev’s cautionary tale is another reason to reject the conceit that the U.S. can identify people on “our side” to arm in another country’s civil war. Insurgents will accept weapons when they are offered, but accepting them doesn’t put them on “our side.” Insurgents that accept American weapons aren’t agreeing to subordinate their goals to ours, and they may not share any longer-term goals with the U.S. beyond overthrowing the current government. There may be a temporary convergence of interests–and in Syria I’m not sure that this has happened–but that is all that it is. Providing weapons to an insurgency may or may not allow it to achieve its goals, but what is certain is that it doesn’t provide the U.S. or its allies with the sort of control they want and expect to have. Arming insurgents in foreign conflict is an invitation to them to use outside support for their own immediate purposes, but it provides the patron with neither control nor gratitude later on. Once we dispense with the illusion that the U.S. can meaningfully influence or control parts of the Syrian opposition by providing them with weapons, it becomes clear how short-sighted and unwise the idea is.