Complex sentence: A private defense agency is a (hypothetical) agency that provides defense voluntarily through the free market without being subsidized through obligatory taxation, and without relying on conscription and other intrusive means of support.
Split into simpler sentences: A private defense agency (PDA) is a hypothetical agency that provides defense voluntarily through the free market. A PDA is not subsidised through obligatory taxation and does not relying on conscription and other intrusive means of support.