Slave inferiority did not lead necessarily to racial inferiority.

In contrast to this, slavery in America was set apart by three characteristics: capitalism, individualism, and racism.
Capitalism increased the degree of dehumanization and depersonalization implicit in the institution of slavery.

While it had been normal in other forms of slavery for the slave to be legally defined as a thing, a piece of property, in America he also became a form of capital.

Here his life was regimented to fill the needs of a highly organized productive system sensitively attuned to the driving forces of competitive free enterprise.
American masters were probably no more cruel and no more sadistic than others, and, in fact, the spread of humanitarianism in the modern world may have made the opposite true.

Nevertheless, their capitalistic mentality firmly fixed their eyes on minimizing expenses and maximizing profits.