In a nutshell

Trading in slaves was a legitimate business. It was sanctioned by the Christian Church which benefitted immensely from it. The following countries were key players in the complex and brutal system where European traders would exchange goods such as weapons, alcohol, and textiles for slaves captured or sold by African traders and leaders. The slaves were then transported across the Atlantic in appalling conditions and sold in the Americas, where they were forced to work on plantations, in mines, and other industries. 

Portugal

Portugal was a pioneer in the trans-Atlantic slave trade, starting in the 15th century. Portuguese traders transported African slaves primarily to Brazil and their colonies in the Caribbean.

Spain

Spain participated in the trans-Atlantic slave trade, shipping African slaves to its vast American empire, including the Caribbean, Mexico, and South America, from the early 16th century.

England

England became a major player in the slave trade in the 17th century, transporting millions of Africans to work on plantations in the Caribbean and North American colonies.

France

France was heavily involved in the trans-Atlantic slave trade, particularly in the 17th and 18th centuries, transporting slaves to its Caribbean colonies like Saint-Domingue and Martinique.

Netherlands

The Netherlands engaged in the trans-Atlantic slave trade primarily in the 17th century, sending African slaves to their colonies in the Caribbean and South America, such as Suriname.

Denmark

Denmark participated in the trans-Atlantic slave trade on a smaller scale, transporting African slaves to its Caribbean colonies, including the Danish West Indies (now the Virgin Islands).

Sweden

Sweden was involved in the trans-Atlantic slave trade briefly in the 17th and 18th centuries, transporting African slaves to its Caribbean colony of Saint Barthélemy.

For there they that carried us away captive
Required of us a song;
And they that wasted us
Required of us mirth, saying,
Sing us one of those your beautiful songs.
Now how shall we sing such a song
In a strange land?