The anarcho capitalist answer to military seems to be private defense agencies (PDAs).

https://en.m.wikipedia.org/wiki/Private_defense_agency

In reading through this page, it discusses the dilemma of the “free rider.” This is a person who does not pay for defense services for themselves, but still receive defense benefits from their neighbors who do. Rothbards answer is to say “who cares?” And you know. That’s interesting. I don’t really have a response to that right now except to say, I think it’s a bad incentive, and we all know incentives matter. It would become a game of chicken and the egg to see who could get away without paying for defense, often with the poorest of us the likeliest losers. Also, the defense agency will have less resources, and be worse, without everyone paying for it. 

The page also discusses how corporations would need, and be able to afford, the most defense. So now imagine Amazon is paying for 90% of the services of a particular agency; in other words, 90% of the revenue of that PDA is from Amazon. Essentially, that PDA is completely beholden to Amazon; if Amazon goes down, then they go down. Amazon has a military. Is anarcho capitalism just building corporatocracy? Is that the land scape we want to live in? A land owned by corporations? What are the possible negative or positive ramifications of this? To what extent would Amazon just “do it themselves” and integrate defense into their own business model (armored trucks for example)? And do we want private companies militarizing themselves? Does that make companies worse since they can’t specialize and must be a jack of all trades? 

Finally, in the anarcho capitalistic opines, are other states around the globe just non existent? The Wikipedia page discusses how the PDAs would be mostly set up for defense, with markets choosing to minimize offensive strategies (although no arguments are given as to why this might be the case). Would a PDA, or collective group of them, be able to go to war with an adversarial state like Russia, China, or the Middle East? 

 Nozick discussed this phenomenon in his book in 1974; basically at some point, one PDA becomes dominant and one way or the other transitions to become a state of a sort (what Nozick calls the ultraminimal state...)

https://en.m.wikipedia.org/wiki/Anarchy,_State,_and_Utopia 

 Hermann-Hoppe, in “Democracy — the God that Failed,” openly advocates for PDAs to destabilize and even attack nations in order to destroy their monopolistic competition. 

 In a world with an open market of PDA’s, where there is no monopoly, and there is competition amongst the various PDA’s, how is consensus reached on the market to make a coordinated attack? How do customers “vote” to attack and destabilize a nation, and is there reason to believe that an uncoordinated attack would always work? Say that a single PDA had a fraction of the US military’s might; how effective is this against an entire nation? 

I feel like the problem with these scenarios and questions is that’s it’s all theoretical. We could come up with examples of where PDAs might work, and can equally come up with examples of where they don’t and couldn’t work. But it feels like there is a degree of hubris required among ancaps to claim with any degree of certainty that they definitely would work as a viable alternative to a states monopoly of a military. 

 That also seems to go against the non aggression principle, no? Attacking a nation that didn’t attack you just to destabilize it? 

 Yeah, I think there’s some tension here. We tend to say we are against any form of physical violence. But then restricting access to resources can be interpreted as violence in the physical realm. “Threatening our way of life” is another gray area. So I can see a situation where a group feels threatened in a way that could prompt an attack from a PDA that claims to be nonviolent.