Europe was a backwater of civilization around 1500. China and India had the world's largest, most successful economies. Turkey was the great military power. To expand their powers the kings of Portugal and Spain turned to piracy. Spain pirated the "new world" of the Americas. Portugal grabbed the African coastal areas and Brazil. All this was done with the blessing of the Pope, who took his cut of the plunder.
In eastern Africa a number of cities were thriving centers of trade between the African interior, which produced gold, iron, and ivory, and eastern Asian producers of cloth and other finished goods. These cities were located in what are now the countries of Somalia, Kenya, Tanzania and Mozambique. Islam was the prevailing religion.
Vasco da Gama commanded the first Portuguese ships to enter the Indian ocean, sailing all the way to India in 1498. On the way he stopped at east African cities. "De Gama and his sailors were astonished by the wealth and comfort they found there." The Portuguese could have become immensely wealthy simply by trading, but instead they chose to use force to plunder the existing cities. One witness in 1505 wrote: "In Kilwa ... as soon as the town had been captured without opposition, the Vicar-General and some Franciscan priests came ashore, carrying two crosses in procession. They went to the palace, and there the cross was set down and the commander prayed. Then everyone started to plunder the town of its goods." In Mombasa the looting was followed by burning and killing all the residents who had failed to flee.
Portuguese power in the Indian ocean was fading by 1600. But meanwhile they had managed to destroy a great civilization based on peaceful trade.
Facts and quotations in this section are from A History of East and Central Africa to the Late Nineteenth Century by Basil Davidson, Doubleday - Anchor books, 1969.