The slavery was a peculiar institution because the slaves used to show in the market as goods where they presented a pen or non-living things in the row.
Explanation:
The expansion and high demand of cotton increased the demand of labor. These workers (salves) were not paid by their owners. Their owners used them as a commodity and not as human being. They used to work for long working hours without any leave or other facility at the work place.
An idiom is a funny saying/phrase. It does not serve as any criminal law or military action. It doesn't mean a foolish person, but it is just an artistic style used in some texts.
