Early African kingdoms such as Ghana (800s-1000CE) and Mali (1200-1450CE) made most of their wealth by

-selling slaves to the Portuguese.

-trading gold across the Sahara Desert.

-trading salt for silk across the Indian Ocean.

-raiding European ships sailing in the Atlantic.

A succession of powerful kingdoms in West Africa, spanning a millennium, are unusual in that their great wealth is based on trade rather than conquest. Admittedly much warfare goes on between them, enabling the ruler of the most powerful state to demand the submission of the others. But this is only the background to the main business of controlling the caravans of merchants and camels.

These routes run north and south through the Sahara. And the most precious of the commodities moving north is African gold.

The first kingdom to establish full control over the southern end of the Saharan trade is Ghana - situated not in the modern republic of that name but in the southwest corner of what is now Mali, in the triangle formed between the Senegal river to the west and the Niger to the east.

Ghana is well placed to control the traffic in gold from Bambuk, in the valley of the Senegal. This is the first of the great fields from which the Africans derive their alluvial gold (meaning gold carried downstream in a river and deposited in silt, from which grains and nuggets can be extracted).

Like subsequent great kingdoms in this region, Ghana is at a crossroads of trade routes. The Saharan caravans link the Mediterranean markets to the north with the supply of African raw materials to the south. Meanwhile along the savannah (or open grasslands) south of the Sahara communication is easy on an east-west axis, bringing to any commercial centre the produce of the whole width of the continent.

While gold is the most valuable African commodity, slaves run it a close second. They come mainly from the region around Lake Chad, where the Zaghawa tribes make a habit of raiding their neighbours and sending them up the caravan routes to Arab purchasers in the north.

Other African products in demand around the Mediterranean are ivory, ostrich feathers and the cola nut (containing caffeine and already popular 1000 years ago as the basis for a soft drink).

The most important commodity coming south with the caravans is salt, essential in the diet of African agricultural communities. The salt mines of the Sahara (sometimes controlled by Berber tribes from the north, sometimes by Africans from the south) are as valuable as the gold fields of the African rivers (see Salt mines and caravans). Traders from the north also bring dates and a wide range of metal goods - weapons, armour, and copper either in its pure form or as brass (the alloy of copper and zinc.