Interesting reading, Civilian control of the military:
"The purpose of the military is to defend society, not to define it."
"The danger of granting military leaders full autonomy or sovereignty is that they may ignore or supplant the democratic decision-making process, and use physical force, or the threat of physical force, to achieve their preferred outcomes."
"Civilian leaders cannot usually hope to challenge their militaries by means of force, and thus must guard against any potential usurpation of powers through a combination of policies, laws, and the inculcation of the values of civilian control in their armed services."
See also Separation of powers