A recent study by the Rand Corp. explains some of the consequences of this shift. Civilians exercise less control over the military because so few now serve. The militia ideal of the founding era, or even the citizen-soldiers who won the world wars, has disappeared. As a result, military service is less obligatory, less universal and less civilian than it has ever been in U.S. history.
It would appear we have abandoned the constitutional vision that defined who we are and served us so well for over two centuries. Historically, republics suffer when they do not expect their citizens to fight or cannot find enough of them willing to do so, which has been a recent problem as most branches of the military struggle to meet their recruitment goals. Historically, this is symptomatic of a debilitating disease — a lack of civic commitment — that could kill the republic. In ancient Greece, city-states such as Athens and Sparta that created republics defended by average citizens devolved into a mercenary culture, then were conquered by the Macedonians.
The Roman Republic conquered the Mediterranean with citizen-soldiers. The republic decayed, however, and when tyrants turned it into an autocracy, the first Roman emperor transformed the army into a professional corps loyal to him alone. Citizen-soldiers were just too dangerous for an autocrat.