Why did so many cheap slaves appear in Rome? What was the main difference between a slave and a free one?

The main reason for the abundance of slaves in ancient Rome, which led to a decrease in prices for them, is the endless wars of the Romans. For them it was a frequent occupation to sell conquered peoples into slavery, sometimes the population of an entire city. This all led to the fact that there were more slaves than they were needed. The main difference between a slave and a free one was that the former were not free, did not decide their fate, could not choose the type of activity, refuse to work, did not receive a salary, they were given little food, etc.