Well....no matter what the reason (cutting military budgets, increased international pressure, a new push for isolationism from voters)...the biggest impact is economic.

America has the second largest standing army in the world at just over 1.3 million active duty service members. Unless you wanna put all of our armed forces on border patrol detail (unlikely and probably impossible), a close in overseas bases results in a sizeable drawdown. Insterestingly enough, the US really doesn't have all that many of its troops overseas, roughly 160,000. However, the minute we pull them back that's 160,000 people that are looking for new jobs, so unemployment numbers skyrocket.

Otherwise, it might actually be a positive thing in terms of international diplomacy. The presence of American troops is a strain on relations with many countries. South Korea is a really good example of this, but I figure all countries would really rather the US troops be off their soil. This could be the first steps in combating the growing worldwide sentiment of general distrust of a "meddling" America abroad.

The military's argument against this, beyond the economic impact, would likely involve our ability to react to threats against our interests around the globe. Take our German bases: they house both our European command and our Africa Command. During the Libyan conflict, the proximity of our German bases to the conflict allowed us to much more easily monitor and handle the situation. Removing our bases would remove the possibility of "Rapid Response" to critical situations.

The counter argument to this is that, in this day and age, is it really that much different? We live in the age of instantaneous information, data can be sent in seconds. Flights across the pond, while taking 8ish hours, are still relatively quick. Rapid response would become a matter of international cooperation rather than unilateral action by America.

Just a few points of consideration.