That is false. A free market is properly defined as a market where the use of force is barred by the government. So when the government itself initiates force

That is false. A free market is properly defined as a market where the use of force is barred by the government. So when the government itself initiates force in the market, it is not a free market. There is no such thing as a monopoly without the use of force. You can temporarily have companies that have a very large share of their respective markets, but monopoly is not properly defined as "a very large company." A cartel is just an opportunity for other people to make money by undercutting the cartel. For instance, if the cartel is maintaining artificially low wages, the competitor can take advantage by paying "normal" wages and getting the best employees. Hence, a cartel is not stable. (Unless it has government force backing it---as all modern successful cartels do.)