The US military is currently maintaining a status quo around the world, including preventing military aggression against smaller democratic nations and keeping shipping and international trade open and equal for the participation of more nations. Conversely, the US military is very expensive for American citizens to maintain and is a great source of anti-American sentiment, as the US is meddling in all nations' international and often internal affairs.
Libertarians propose that a good solution to reduce the nations debt and end the US's unending series of wars is to reduce the US's military influence globally by reducing the number of bases in foreign countries and withdrawing from traditional areas of hegemonic influence, such as in South Korea.
When I ask libertarians what will happen to countries dependent on the US military, mostly I get response of: it's not a concern or its not the US's business anyway. But have there been solutions proposed for how American allies greatly dependent on US military influence will pivot diplomatically and militarily to evolve to these changing circumstances? Perhaps an academic has attempted to answer this question specifically, but if not:
Edit: Nations I am seeking information on. I do not expect answers to include all requested information: Germany, France, South Korea, or Japan
Politically, how would Japan and/or Germany transition to normalizing use of military forces as they currently are using "defense forces."
How much would defense budgets need to be increased to make up for complete withdrawal of American military involvement in these regions?
Are current military/diplomatic alliances in these regions adequate to countering potential aggression, especially considering that aggression and disputes over borders, shipping lanes and natural resources may increase with the withdrawal of the US?