The libertarian position of Foreign Policy is basically the same position as for anything else: "Leave me the hell alone and I'll return the courtesy."
Libertarians also generally don't believe in the "measured response". If someone tries to rob you at knifepoint you don't evaluate the proper level of force in responding, you shoot him in the head, pee on his corpse, and if possible set his head on a pike as a warning to others that you don't do that.
So. when it comes to Foreign policy there are basically three options: Democrat-style appeasement, Republican-style nation building, Libertarian-style non-intervention.
Option A means ultimately going gently into that good night, and loosing our position of leadership in the world. But at least people will like us, right?
Option B, put bluntly, means eternal low intensity conflict as we police the world. Because at the end of the day, it's not actually possible to win a "War against Terror". Or Drugs, or Abortion, or ...
Note that most D's and R's are happy to mix the A & B in their own preferred proportions.
Option C probably means decades of peace punctuated by periodic high intensity warfare.
Remember, Libertarians don't want to ignore the world as much as they want it to leave them alone. Take Afganistan as an example:
A) Democrat solution: try to use international courts and diplomacy to bring the perpetrators to "justice".
B) Republican solution: wage an undeclared war, then set up a "friendly" government so they won't do that again. Oh yeah, it might take a while (like 20 years).
C) Libertarian solution: Bomb the place back into the stone age, then drop leaflets that say "y'all are free now, try to set up a better government next time". Don't make us do it again or we'll charge you for the bombs.
We wouldn't really send them a bill for the bombs. Ok, some of us might.
Regardless, the Libertarians really believe that one can't spread democracy at the point of a bayonet. We're willing to kill your dictatorial thugs off for you (especially after they have torqued us off) but setting up a government that respects individual rights, follows the rule of law, etc. is your own bloody responsibility.