(2) Huge numbers of native workers died of diseases imported from Europe, to which they had no resistance
(3) Imported European workers working for pay quickly accumulated enough money to become landowners and hire their own workers
(4) Central Africa was in almost constant constant tribal warfare, and it was traditional for the losers to be enslaved by the winners. Beginning in the 1500's some alert Portugese traders realized that they could buy slaves from the successful coastal tribes and transport them to the Americas as workers. This allowed Portugal to establish thriving sugar plantations in Brazil.
(5) The Atlantic Slave Trade grew and slaves were move from inland Africa to the coast to feed the trade. Most of the early slave trade was conducted by Portugal and Spain, but by the 1600's Britain was the leading operator of slave ships, carrying slaves to the West Indies and later a few to British North America.
(6)There were so many crops that were prized in Europe that could only be grown in the tropical and subtropical Americas, especially sugar and cotton.
(7) The Spanish crown would not allow natives in Mexico, Central, and South America to be enslaved at first.
(8) Being more naturally resistant to diseases such as malaria, Africans could be worked harder and were more productive than native people.
When you say "in America", you do need to realize that out of the more than 10 million African slaves who lived to reach the Americas, only about 600,000 were in what is now the USA. The vast majority of African slaves involved in the holocaust of the Atlantic Slave Trade went to Brazil and the islands of the West Indies.