Small doesn't mean non-existent. One of the few things even the most extreme anarcho-capitalists believe the government should do is protect it's people from a hostile takeover on behalf of a non-anarcho-capitalist nation.

Well, I don't think any sane country will try to invade somewhere where the citizens have recreational nukes.

Nukes don't defend a country without a huge human force supporting and maintaining them.

In addition to that, you need to constantly evolve your delivery vehicles to overcome newly developed defense capabilities.

In even the most bare-bones defense scenario, the needed investment is fairly large, and it depends on how large of an investment adversaries make.

I think that most anarcho-capitalists don't believe in a government or nation.

Sure they do. They just call countries "collectives."

Anarcho-capitalists just want archipelagos of privately-owned governments.