What are the positives and negatives of The Columbian Exchange?

How was rockefeller able to build his monopoly across the oil industry? he found newer and cheaper ways to refine oil, increasing his profits. he confined his business to ohio so he could buy all the refineries there. he bought up oil refineries, cut costs, and reinvested his profits in other refineries. he began to sell kerosene as well as oil, expanding his market.

True or false: abraham lincoln delayed the emancipation proclamation to make sure the border states would stay loyal. *

What are the contributions of the byzantine empire