Why did spanish settlers turn to african slaves to provide the labor for their american colonies?

What do the discoveries of shells used in jewelry and a huge dredged canal tell us about the indus valley civilization?

Considering the benefits and drawbacks of the different types of money as well as the gold standard, do you agree or disagree with the us government’s decision to discontinue the gold standard? justify your response.

The 20th amendment, also called the lame duck amendment, decreased the amount of time between the presidential election and the inaugration of the new president. what are the advancements that allowed for this amendment?