The Islamic kingdom of Mali was fabled in the Middle Ages for the wealth of its rulers, for the beauty of buildings and artworks created by gifted artisans and for attracting some of the great and wise men of the age.

Reachable only by an arduous trek across the desert, this sprawling kingdom in western Africa south of the Sahara owed its wealth to gold.

The most famous of Mali's rulers was Mansa Musa, whose pilgrimage to Mecca (or Hajj) in 1324 was itself the stuff of legends. According to chroniclers at the time, Musa's caravan brought 60,000 men including 12,000 slaves, and 80 camels loaded with 300 pounds of gold each. Directly in front of the mounted emperor were 500 slaves, each with a gilded sceptre.

Mansa Musa gave away so much gold during his pilgrimage that the Cairo gold market did not stabilize for 12 years.

Mali was one of several empires in Africa during the Middle Ages that in wealth and power equaled anything in Europe. But by the end of the 19th century, those empires and others in Africa had vanished, their glory forgotten. Cities like Timbuktu, once one of the wonders or the world, were crumbling, and the "Dark Continent," as it was called, lay under the domination of colonial rulers like Britain and the Netherlands.

What happened?

The simple answers, slavery and European colonialism, are part of the truth, but they oversimplify hundreds of years of contact between Europe and Africa. Until the beginning of the 15th century, that contact was sporadic and second-hand.

In 1441, a ship arrived in Portugal from Africa carrying gold dust. The news vindicated explorations sponsored by Henry the Navigator, a Portuguese prince who sent ships to explore the African coast in search of a new route to the Spice Islands in the East. The traditional routes were blocked at the eastern end of the Mediterranean by the Ottoman Turks, who were hostile to the Christians of Europe and whom Henry hoped could one day be attacked from behind and defeated.

As successive explorers pushed down the coast, trade with coastal African peoples increased. As a result of this shift in trade, Mali's network of Saharan trade routes lost its luster, and Mali itself went into decline.

"As European contact increased, there was a ... reorientation toward the coast," says Clifton Crais of Kenyon College. "Ultimately, Afro-European contact reshaped those states and destroyed quite a few."

Mali, whose grandeur was the stuff of legends, had undergone a steep decline by the time the first Europeans saw it for themselves in the 1450s. The Europeans' underwhelmed reaction -- this is the best Africa can offer? -- would color Western assumptions on Africa for centuries to come.

With Mali in decline, much of its empire fell under the control of the Songhai. Central to the Songhai Empire were the trade and cultural hubs of Djenne, Goa and Timbuktu, which were fading along with the trans-Sahara trade.

Another development, this one in trade, would shape the future of Africa and the Americas to the present day.

Just one year after that first shipment of gold arrived in Portugal, another arrived, this one accompanied by human cargo -- 10 Africans. Looking for gold, the Portuguese had found slaves.

Slavery was not invented in Africa. It has existed, at various times and in various forms, since the beginning of recorded history, and in Africa the practice predated Europeans' arrival: Africans enslaved other Africans.

Portugal enjoyed a virtual monopoly in trade with the Africans for a century and a half, obtaining gold by trading cloth, copper, and iron -- and by transporting slaves from one part of Africa to another. They found customers in the Ashanti kingdom, in what is now Ghana.

"Up until the 18th century, the Ashanti kingdom imported slaves," Cais says. "What the Portuguese and other Europeans were mainly interested in was not slaves at all, but in Ashanti gold. ... The Ashanti kingdom traded gold for slaves."

Portugal, facing a labor shortage, received the first exported slaves. The Americas, with abundant land and a scarcity of workers, was a much larger market. In the 17th century, the slave trade became a transatlantic affair and steadily gained momentum for the next two centuries.

The slave trade expanded rapidly to meet demand in the New World, and the kingdoms that arose were more reliant on slave exports.

"The classic example of a political kingdom that was literally founded on the slave trade is the kingdom of Dahomey," Cais says. "It rose and fell on the slave trade."

No one is sure how many Africans were brought to North America and the Caribbean. Estimates range from 10 million to 60 million. Shackled, crowded below decks in horrific conditions, often poorly fed, hundreds of thousands perished before they ever reached the New World.

The impact on some areas of Africa was profound. In Angola, for example, Europeans' preference for male slaves left the population with far more women than men. On the fringes of the slave-trading kingdoms, some areas became entirely depopulated.

Paradoxically, while the slave trade played havoc wth the people of Africa, some scholars believe it was the end of commerce in humans -- nearly all of Europe outlawed the slave trade by the early 19th century -- that spelled the end of the coastal kingdoms.

"In general, the ending of the Atlantic slave trade sent very serious shock waves throughout western Africa," Cais says. "Kingdoms like Dahomey and Oyo literally fell apart."

In the latter half of the 19th century, some Africans tried to defy a slave-trading ban that was imposed and enforced primarily by Britain, while others simply wanted to rid themselves of European domination. But by then it was too late.

Throughout the period when the slave trade was thriving, European presence in Africa steadily increased. Attracted first by gold and slaves, they turned their attentions to the continent's other resources, establishing outposts and sending troops to enforce their claims.

Some African states had offered resistance, but none that was a serious impediment to plunder. Queen Nzinga of the Ndongo kingdom, in what is now Angola, went to war in 1623 rather than supply the number of slaves the Portuguese demanded. Other kingdoms, notably Benin and Congo, also fought against the slave trade for a time but did little to stop the plunder.

The last gasp of African independence was the Zulu state, in what is now South Africa. In 1879, the Zulus went to war with the British, who had machine guns and other modern weapons of war. Although they won a surprise victory at Isandhlwana, the Zulus were quickly defeated.

The Zulu state was "a remarkable and very strong state for Africa, but it was insignificant" compared to European states, says Julian Cobbing of Rhodes University in South Africa. "It was crushed by the European invasion very easily, give or take the winning of a military engagement or so."

At no time was there unified resistance to European influence. Africans did not regard the Europeans as any more "alien" than their African neighbors, and the notion of a pan-African resistance to the Europeans simply never occurred to them.

"The idea of 'us' and 'them' is definitely a 20th century [idea]," says Stephen Orvis of Hamilton College. "Identity is formed out of a set of experiences, and the idea of Africa vs. Europe only develops over the course of the slave trade and colonialism."

In part because of colonial boundaries that ignored tribal affinities and forced people together in spite of old animosities, that unity among Africans is still difficult to come by, even within national boundaries. Nation-states -- countries with common bonds and a stable government -- have been difficult to form in Africa, some scholars say.

"How can you get a nation-state emerging overnight?" Cobbing asks. "It'd be quite impossible. Nation-states took two or three hundred years to evolve in Europe. What you got in the 1960s was the myth of African nationalism."

"We still don't have any [nation-states], even today," Cobbing says.

As a result, centuries after the kingdoms of Mali, Songhai and Great Zimbabwe brought order and prosperity to their regions, Africa is now divided into regional entities whose future is still uncertain.