Question

why. had. europeans called Africa as. dark continent

Answer 1

The term "Dark Continent" seems to have been a concept began at least as far back as the sixteenth century, and it denoted unexplored, little known, or uninhabited terrain or even academic areas. When one looks back into history, the concept was also applied to places like South America or very cold and night-ridden places like Greenland. But over time, the concept became more significantly applied to Africa. The Europeans regarded Africans as very different from and ignorant of the rest of the world. The black Africans were denounced for not embracing world religions, but being steeped in human and animal sacrifices, superstitions, blood rituals, witchcraft, ancestral worship and veneration, and in polygamy. They were regarded as underproductive and little concerned about the future and development. Their infrastructure was poorly built, many lived in huts and hovels. Africans were also regarded as backward because they wore little or no clothing, slung babies on their backs, prostrated themselves or groveled before their kings, they could be executed at the pleasure of their kings and had very little power and say in the face of kings who were regarded as demi-gods. the women did nearly all the domestic work while the men were mainly hunters and warriors. Also, a lot of Africa was wilderness of jungles and animals; and of tropical diseases and parasites. Many europeans were felled by maladies such as malaria. The situation reached horrendous levels during the slave trade when alcohol and guns were imported into Africa, and inter-group and even inter-neighbor warfare reached it's apex during the slave-trafficking and also commerce in ivory. People traded their enemies, neighbors, and even relatives for cloth, beads, guns, and even things that were nearly worthless. Slave traders favored chiefs and kings whom they would arm to help them capture people to be enslaved. Black Africa became regarded as an unsafe and dangerous place to live in during that time.

Answer 2

Africa got the name ' dark continent ' in the 19th century by the Europeans as they themselves weren't aware much of their own country. It's land, riches, resources etc.... 
So that's why they were called so.
Thanks