From Into Africa: The Epic Adventure of Stanley and Livingstone, by Martin Dugard (Broadway Books, 2003), Kindle loc. ~1100:
Then, just when things looked their worst, Livingstone’s life was saved by the people he despised most. On February 1, 1867, he encountered a band of Arab slave traders. They took pity on the destitute, failing traveler, and gave Livingstone food to restore his strength. He accepted it without a second thought about the compromise he was making. Before the Arabs could leave, Livingstone wrote to the British Consulate in Zanzibar, begging that a second packet of relief supplies be sent to Ujiji, where he would meet them. Livingstone’s supply list read like a starving man’s fantasy: coffee, French meats, cheeses, a bottle of port. With his original supplies so depleted, this additional shipment would be vital. The Arabs accepted his letters and promised to deliver them.
Livingstone’s compromise seemed relatively minor—accepting food for himself and his starving men, entrusting his mail to their care—but showed how greatly the search consumed him. Few men of his era spoke out as passionately against slavery as Livingstone. To eat food that was paid for with money earned from slavery was against everything for which he stood.
In his journal there was no attempt at rationalization, just a matter-of-fact admittance that he’d come across a caravan led by a slaver named Magaru Mafupi. The slaver was a “black Arab,” born of an Arab father and African mother.
The lineage might have confused the outside world, but Livingstone knew well the symbiotic relationship between Africans and Arabs. Although Europeans perceived the African continent to be an uncharted land populated by indigenous cultures, the truth was that Arabs had lived alongside Africans for over a thousand years. It was the seventh century A.D. when Arabian ships began trading beads for ivory with Bantu tribes along the East African coast. A mingling of their cultures began: The Arabs brought Islam; Swahili, meaning “coastal,” was formed by merging Arabic and Bantu; the financiers of India and Persia set up shop in Zanzibar to outfit caravans; African men found work hauling ivory, giving birth to the occupation of pagazi—porter. Little boys of the Nyamwezi tribe even carried small tusks around their village, training for the great day when they would join the mighty caravans.
That relationship between Arab and African had been corrupted, though, as slavery became lucrative in the sixteenth century. Losers in war were routinely enslaved, and children were often kidnapped as their parents worked the fields. As early as the seventh century, men, women, and children from subequatorial Africa were being captured by other African tribes and spirited north across the Sahara’s hot sands. Two-thirds of those surviving the epic walk were women and children about to become concubines or servants in North Africa or Turkey. The males comprising the remaining third were often pressed into military service.
That slave trade route—known as the Trans-Saharan—was augmented by the opening of the East African slave trade a century later. Instead of Africans, it was the Arabs driving this new market, focused mainly along the easily accessible coastal villages. They found that slaves were a more lucrative business than gold and ivory, and began capturing clusters of men and women for work as servants and concubines in India, Persia, and Arabia. Even with the second slave route open, slavery was still not a defining aspect of African life, but a gruesome daily footnote. When the Portuguese came to East Africa in 1498, however, and as other European colonial powers settled the Americas during the following century, that changed. Slavery became the continent’s pivotal force. By the end of the sixteenth century, England, Denmark, Holland, Sweden, and France had followed Portugal’s initial example, and pursued slavery as a source of cheap labor and greater national wealth. A third slave trade route—the transatlantic—opened on Africa’s west coast. Slaves bound for America, the Caribbean, South America, Mexico, and Europe were marched to the west coast ports of Luanda, Lagos, Goree, Bonny, and Saint Louis, then loaded on ships for the journey.
Great Britain’s economy became so dependent upon slavery that some maps of western Africa were divided by commodities: Ivory Coast, Gold Coast, Slave Coast. But as Britain began to see itself as a nation built on God and morality, and as it became savvy for politicians to align themselves with the growing Christian evangelical movement, slavery was abolished in all British colonies and protectorates in 1834. During his first trip to Africa in 1841, Livingstone was terribly unaccustomed to the sight of men, women, and children being bought and sold. As he insinuated himself into the fabric of African life over the years that followed—speaking with the natives in their native tongue wherever he went, sleeping in the villages during his travels, making friends as he shared meals and nights around the campfire—the barbarism of the practice incensed him even more. He grew determined to stop it.
Livingstone’s focus was on the east coast, where Portugal had supplanted the Arabs as the coastal region’s reigning power. Even as other nations slowly abandoned the practice on humanitarian grounds, slavery became the cornerstone of Portugal’s economy. The tiny nation exported African men and women by the hundreds of thousands from ports on both the east and west coasts of Africa. African tribes were raiding other tribes, then selling captives to the Arabs in exchange for firearms. The Arabs, in turn, marched the captives back to the east coast, where they were either sold to the Portuguese or auctioned in Zanzibar. The slaves were then shipped to Arabia, Persia, India, and even China.