The Atlantic slave trade or transatlantic slave trade took place across the Atlantic Ocean from the 16th through to the 19th centuries. The vast majority of those enslaved that were transported to the New World, many on the triangular trade route and its Middle Passage, were West Africans from the central and western parts of the continent sold by other western Africans to western European slave traders, with a small minority being captured directly by the slave traders in coastal raids, and brought to the Americas. The numbers were so great that Africans who came by way of the slave trade became the most numerous Old World immigrants in both North and South America before the late 18th century. Far more slaves were taken to South America than to the north. The South Atlantic economic system centered on producing commodity crops, and making goods and clothing to sell in Europe, and increasing the numbers of African slaves brought to the New World. This was crucial to those western European countries which, in the late 17th and 18th centuries, were vying with each other to create overseas empires. The Portuguese were the first to engage in the New World slave trade in the 16th century, in 1526, and other countries soon followed. Ship owners considered the slaves as cargo to be transported to the Americas as quickly and cheaply as possible, there to be sold to labour in coffee, tobacco, cocoa, sugar and cotton plantations, gold and silver mines, rice fields, construction industry, cutting timber for ships, in skilled labour, and as domestic servants. The first Africans imported to the English colonies were classified as "indentured servants", like workers coming from England, and also as "apprentices for life". By the middle of the 17th century, slavery had hardened as a racial caste; they and their offspring were legally the property of their owners, and children born to slave mothers were slaves. As property, the people were considered merchandise or units of labour, and were sold at markets with other goods and services. The Atlantic slave traders, ordered by trade volume, were: the Portuguese, the British, the French, the Spanish, and the Dutch Empire. Several had established outposts on the African coast where they purchased slaves from local African leaders. These slaves were managed by a factor who was established on or near the coast to expedite the shipping of slaves to the New World. These slaves were kept in a factory while awaiting shipment. Current estimates are that about 12 million Africans were shipped across the Atlantic, although the number purchased by the traders is considerably higher.