Portuguese sailors were the first men of Europe to explore the west coast of Africa and go round the Cape of Good Hope; and in the three centuries before 1800 they were by far the most active adventurers in Africa. They were so, not only because they had discovered Africa, but because they (and the Spaniards) had suffered so cruelly from the Muslims that they were always anxious to reduce their power.
And after they had driven the "infidels" out of the Peninsula, they crossed over the sea to try to conquer the "infidels" of North-West Africa, which they knew was once part of the Roman Empire, and had once been Christian.
But in these wars they had little success. So they were forced to go farther and farther south on the coast of West Africa in the hope of getting round these Muslim countries, and perhaps finding the Christian kingdom of Prester John, about which every boy had heard many strange and exciting tales. By Prester John they most likely meant the king who reigned over Christians in Abyssinia, who had held the heathen and Muslims at bay for hundreds of years, just as the legends said Prester John did.
Perhaps the chief reason for the interest which the Portugnese took in Africa was to find a safe way of reaching the riches of India. Until the Suez Canal was open, this was the main advantage which the Dutch and the British also sought to gain from possessions in Africa.
But before the Portuguese could feel sure that their voyages to India were safe, they had to fight a strong Muslim power on the east coast of Africa, where skilful Arab sailors carried on a profitable trade in Slaves, as well as in other things, between Africa and Asia. This Arab power was quite as much a foreign invader as any European people. It treated the natives with more brutality, and caused more distress, than any other invader (except perhaps the Belgian rulers of the Congo in the nineteenth century).
Many dangers faced any Europeans who tried to colonize or to conquer, or even to explore, the interior of Africa. The Africans had extremely powerful kingdoms in the centre of the continent. Some in the Sudan and in the Sahara had set up great empires, especially those who had been influenced by the Arabs from Asia, and had married with the Arab tribes.
Timbuktu was the most famous of these states. Most of the explorers who tried to travel across North Africa were killed by their fierce peoples, or by the fiercer tribes who wandered over the whole land.
Even where Muslim and Arab influence had not been able to reach -- even south of Lake Chad -- obstacles almost as serious were in the way. There were impassable forests and dense jungle; fever marshes, and a deadly climate -- most deadly along the river valleys, which offered almost the only way of approaching the interior. The people were hostile, and even where they were inclined to be friendly, the conditions of life were almost enough to prevent Europeans from settling. It is, then, not surprising that for 300 years the map of Africa was almost a blank, and that it was known as the Dark Continent.
But Africa was hardly made a real part of the world as known to the peoples of Europe before the beginning of the nineteenth century, though, as a result of what was done in that century, Europe will probably have even more influence in Africa than it will ever have on Asia.