How do you avoid monopoly?
If you mean the business type, then competition is the answer. If you are the competition, then offer the customers better than the main competitor. If you are the monopolizer, then good.
The difference between the term 'monopoly' and 'natural monopoly' is a monopoly is a market situation one group controls the availability and price of a service or item. A natural monopoly is a service or item that is provided by a single sorce. An example would be transportation like buses, or taxies.
Some of the differences between Monopoly and Monopoly City is that in Monopoly city you can start building on a property immediately. Another difference is that in Monopoly City there are different types of buildings. in Monopoly City there are residential building, Industrial buildings, Stadiums, Skyscrapers, Bonus buildings (ex. schools) and Hazards. The use of special board spaces, chance cards and railroad are different as well.