What was the slave trade?

The slave trade was a system created for transporting native Africans to North and South America to be used as free labor.  Most slaves came from the western part of Africa.  Once in the New World, slaves were sold at auctions and used to plant and harvest crops and as domestic servants.  
The Portuguese began transporting slaves from Africa to the New World in the 1400s.  Other European nations soon joined the slave trade.  Sometimes slaves were sold by fellow Africans to slave traders.  Other times they were captured by the European slave traders themselves.  The slave trade was a profitable business, which was the main reason why it continued.
Conditions on slave ships on the journey across the Atlantic Ocean were usually miserable for slaves being transported.  Many captured Africans were packed into small areas on slave ships.  They were treated more like cargo than humans.  
The Middle Passage was the name of the most common route for slave trade.  This route formed a sort of triangular shape from Africa to Europe and the Americas.  
In the late 1700s, a movement to end the slave trade grew in popularity.  Many people who opposed it were motivated by their Christian beliefs, such as William Wilberforce and Quaker groups.  By the early to mid 1800s, most countries had banned the slave trade.  Some smugglers continued to trade slaves across the Atlantic, but they could be punished if caught.