You might be interested in some previous threads about about the origins of modern racism and racism before the Renaissance:

Ancient Slavery and Racism

• " it should be noted that slavery in the ancient Roman Empire was closer to the modern-day employer-employee relationship, not the slavery of other eras based on kidnapping and racism" some biblical scholar - 47 comments, over 2 years old.
• Specialists on both eras involved engage in comparisons and debate on ancient and early modern slavery.
• "I don't think that ancient slavery is really comparable to the chattel slavery that we saw in the Americas." How did ancient slavery differ from the atlantic slave trade? - 91 comments, over 6 months old.
• This thread is mostly about Roman slavery including how slaves were acquired, what they were used for, and what ethnicity/race they were and thus allowing comparison with the situations presented in the threads above.

Racism and Slavery

• Did Racism Cause the Enslavement of Africans? - 2 comments, over 2 months old.
• The commenters here summarize the matter without going into detail.
• Do you think racism was the result of slavery? or whether africans were enslaved because of racism? - 7 comments, over 8 months old.
• The commenters here go into detail on the genesis of racism in the US from the Thirteen Colonies to the Antebellum United States.
• Why did Europeans enslave Africans instead of other Europeans? - 17 comments, over 2 months old.
• The commenters here go into the difficulties involved in enslaving people in Europe to compare and contrast with the methods used in Africa as well as going into developing attitudes towards race in the Early Modern era.
• How true is the claim that "racism created race", as opposed to the other way around? - 9 comments, over 6 months old.
• This thread brings up and summarizes the a book with a contrary claim to the traditional narrative that modern racism primarily derives from the Early Modern era.

Racism and European Imperialism

• Europe had normal diplomatic relations with non-white nations before turning explosively racist to justify their actions against all others. What happened to cause this shift? - 22 comments, over 1 year old.
• A flaired commenter in this thread provides a multi-comment long overview of the "flowering" of racism and scientific racism in the 18th and 19th centuries at the height of European imperialism.
• What are some of the more notable (scientific) critiques of scientific racism - especially in the 19th century? - 3 comments, over 1 year old.
• A flaired user's description of the opposition to scientific racism also serves to highlight the common racism of the day and its origins.
• When did the concept of Race begin to emerge? - 25 comments, over 1 year old.
• There are a few summaries of "milestones" of the development of racism from the Age of Exploration to Age of Imperialism with a related article linked in the topmost comment.

Racism in Antiquity

• I've often heard it said that the ancient Romans were so culturally and ethnically non-homogenous that "racism" as we now understand it did not exist for them. Is this really true? - 137 comments, over 2 years old.
• This thread dives headlong into the matter, inciting debates over whether the ethnic stereotypes common in the ancient world are of the same kind as modern racism or not while supplying plentiful evidence and analysis for both sides.
• Was there much racism in the Roman Empire directed at people from other regions? - 47 comments, over 1 year old.
• The commenters in this thread differentiate between the xenophobia present the ancient world from the modern understanding of racism.
• I know the Romans had no conception of race, but did they view Black Africans any differently than they did the Persians, Libyans, or Celts? - 80 comments, over 11 months old.
• This thread goes into the way Rome interacted with peoples that would be classified in the modern day as being of different races.
• Racism in the ancient world? - 37 comments, over 1 year old.
• This thread pulls examples from all across the world and its history along with copious amounts of sources for further reading.
• Did the Romans have stereotypes about the behavior of people from particular tribes or geographic areas? - 9 comments, over 11 months old.
• Several commenters detail the most common stereotypes that Romans held of others at the borders of their empire and beyond.

race wasn't really a part of slavery in the Americas even until around the turn of the 18th century, when interracial, class-based resistance movements (bacon's rebellion is the big one) became a huge issue and whiteness began to be privileged in order to create a boundary between the white and black underclasses. Its around this time that you see a slew of laws limiting black people in general to having less freedom, regardless of their freedom status. Keep in mind that white indentured servants could be bought and sold and that native americans were the first slaves in the Americas. Slavery as being reduced to race became a factor after many decades of slavery in north america