Whenever someone asks me how he can learn more about the libertarian perspective on foreign policy, I recommend Chalmers Johnson. Johnson, who recently passed away, was a liberal, not a libertarian. But there are few people who have a better handle on foreign policy from a libertarian perspective than Johnson did. If you want to truly understand the foreign-policy problems facing our country and what we need to do about them, read Chalmers Johnson.
The best thing to do is to read the four books authored by Johnson:
Blowback: The Costs and Consequences of American Empire
The Sorrows of Empire: Militarism, Secrecy, and the End of the Republic
Nemesis: The Last Days of the American Republic
Dismantling the Empire: America’s Last Best Hope
If instead would like to begin reading articles by Johnson, I’ve posted some links below that provide many of Johnson’s articles that are posted online. Undoubtedly there are more but these links will give you a good start. By just reading these articles, you will have an excellent grasp of foreign policy from a libertarian perspective. Then, you can decide whether to go further and read the books.