What was the relationship between racism and slavery?

Racism is "prejudice, discrimination, or antagonism directed against someone of a different race based on the belief that one's own race is superior."

When one believes he/his race is superior, he by default looks down on others. This leads to "prejudice, discrimination, or antagonism directed against someone of a different race" because he doesn't consider their feelings and/or opinions worth as much as his own if not completely worthless. In a case where one considers another as inferior he may even subjugate them.