I have found that this is a recurring topic among libertarians that often appears in the minarchist vs anarchist debate. I recently encountered this great talk on the subject by Prof. Jeffrey Hummel from way back in 1980 that I thought I would share in case anyone is interested. Peace.
"How an Anarchist Society Would Provide National Defense: The Solution to Libertarianism's Hardest Problem"
By Jeffrey Rogers Hummel
This lecture was delivered at the University of Texas at Austin on April 7, 1980. It was recorded by Jim Cartwright, who subsequently marketed it as three audio cassettes. The lecture was recently edited and converted into an MP3 audio file with meticulous care by Bill Courtney.
The audio of this speech was obtained from:
Jeffrey Hummel is a Professor of Economics at San Jose State University:
My blog post on this lecture:
I agree with Prof. Hummel's position in the video. I think some* free market anarchist societies could successfully defend themselves against invasion by foreign states.
I think the minarchist position that the service of "national defense" (defense against invasion by foreign states) can only be successfully provided by a state is mistaken. I think free market anarchist societies would do at least as good a job providing this service as societies with governments (all else being equal), and perhaps a much better job in many cases.
If anyone wants to discuss anything that Jeff Hummel said in the video, or what I just wrote, or anything else related to this topic I would be glad to discuss it with you.
* Some, but obviously not all. For example, "anarchist Luxembourg" would have little to no chance defending itself against the governments of France and/or Germany if those governments and the French and German people wanted to invade Luxembourg and impose a government on the people there badly enough. Of course, if Luxembourg had a state it wouldn't stand a chance defending itself either (assuming all other conditions were the same), and perhaps would stand even less of a chance.
Some other videos/essays I have watched/read on this subject
The Market for Security | Robert P. Murphy (2011) Lecture
Market for Security | Robert P. Murphy (2012) Lecture
The essays "Private Law" and "Private Defense" in Robert Murphy's Chaos Theory.
Robert Murphy's essay But Wouldn't Warlords Take Over?
David Friedman's book The Machinery of Freedom [PDF] (pages 58-83 are especially applicable to this thread)
Murray Rothbard's book For a New Liberty [PDF]
I am currently reading (I'm on page 134 as I write this) Bruce L. Benson's book The Enterprise of Law: Justice Without the State
For other works I've read see here: http://peacerequiresanarchy.wordpress.com/works/
The first time that I was exposed to the subject of Law without Government was this short 3-video series: