I nearly wrote a cranky response along these lines, but then I re-read it. Note the words in bold. Monopoly is about market power, not brute force coercion at point of consumption. The OP made two errors in the use of the word 'monopoly'. This response objected to one, and Multiheaded's response caught another.

I'd also object to your assertion that real-world monopolies are always government enforced. Unless you're being extremely specific in your definition of 'monopoly', or liberal in your definition of 'government enforcement', I do not think this holds up to much scrutiny.