I think the best thing that has been written on the Middle East is Walid Khalidi, ed., From Haven to Conquest. But as a rule of thumb,"When governments are loyal to the US (Israel, Ukraine, etc), the US calls for disarming of all militias and groups that are opposed to those governments. But in the cases of governments that are opposed to the US (Syria, Iran, Cuba, etc) the US funds and arms militias against those governments."