What was the “rectangular” trade and what goods were exchanged

The Slave Trade (398) As they did in Asia, the Portuguese went to Africa to trade. At first, they maintained friendly relations with the Africans. Christian missionaries wanted to convert the continent's residents. Friendly relations soon collapsed, however, as the economic interests of the Portuguese—in gold and, over time, in slaves—became obvious. Despite the fact that Europeans themselves had been slaves in the Byzantine, Arab, and Turkish empires, during the 1500s they began to use slave labor in their own overseas empires. Europeans tried enslaving Native Americans, but the system did not work well due to the devastation of the Native American population caused by disease and the difficulties of enslaving people in their own land. Instead, the Europeans began to rely more heavily on enslaved Africans. The slave trade grew quickly when the Portuguese set up sugar plantations on islands off the coast of Africa. To make a profit, large numbers of slaves were required. Plantation owners got these slaves from the African mainland. Later, the Dutch, English, and French also became active in the slave trade. By the early 1600s the slave trade was the chief focus of European relations with Africa. Triangular Trade Slave trade in the Atlantic was part of a system known as the Triangular Trade. On the first leg of their three-part journey, often called the Triangular Trade, European ships brought manufactured goods, weapons, even liquor to Africa in exchange for slaves; on the second, they transported African men, women, and children to the Americas to serve as slaves; and on the third leg, they exported to Europe the sugar, rum, cotton, and tobacco produced by the enslaved labor force.  Traders referred to the Africa-Americas part of the voyage as the "Middle Passage" and the term has survived to denote the Africans' ordeal. The Middle Passage was brutal and degrading often lasting anywhere from 1-3 months. Traders chained the slaves in the crowded hold of the ship. This stopped slaves from jumping overboard or causing trouble aboard ship.  Branded, stripped naked for the duration of the voyage, lying down amidst filth, enduring almost unbearable heat, compelled by the lash to dance on deck to straighten their limbs, all captives went through a frightening, incredibly brutal and dehumanizing experience.  Slaves had little food or water and no sanitary facilities. Many died before reaching their destination. At the height of the trade in the years between the mid-1700s and the early 1800s, European slave ships carried thousands of slaves each year. It has been estimated that some 10-12 million Africans survived the horrible journey to slavery in the Americas. Many more perished during the horrible journey of the Middle Passage. Others died even earlier, on the hard trip from the African interior to slave ships on the coast.