that if any one man choose to enslave another, no third man shall be allowed to object.in at least one hundred words, define what an inference is and state what inference is being made here about "squatter sovereignty."

I would just state my answer briefly as much as possible. An inference is an educated guess. It is an interpretation you make out of an observation. It does not address the obvious, but it runs deeper to the analytical ability of the human mind. 

Based on the sentence, you can infer that there is a respect when it comes to ownership of slaves. They are bound not to meddle in the affairs of another. This is what may define squatter sovereignty.