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I don't think governments are the only one who could make barriers to entry. Sometimes something as simple as controlling the supply of a commodity is enough to create an insurmountable barrier to entry.
A market with no regulation is more likely to cease to be a free market in the long run than one that is regulated properly with the intention of keeping it free.
The biggest barrier to any market is the initial investment necessary to start a business. The more investment required prior to starting a business the harder it will be for newcomers to enter the market.