How would slaves be controlled in a plantation?
Definitely the brutality mentioned in other answers is correct but if you’re also asking what kept them from escaping the biggest reason was there was nowhere to go unless they were able to make it into a free state. Unfortunately most slaves lacked the ability to read or write much less navigate their way across the slave states to make it to freedom, also according to the law of the time a runaway slave was never free and could be returned to their master at any time and of course the brutality was much worse for a runaway slave than for one who just acted “uppity”.