What caused the change from indentured servitude to slavery?

I think it's because slavery costs less...just a guess.

lincoln declared that slavery should not be allowed to spread into the new states, and of course this angered the south at the time.

c. archbishop desmond tutu promoted the acknowledgement of the rights of black africans and expose human rights abuses.

d. leader haile selassie modernized african society through the institution of progressive social, economic, and educational reforms.