Why was Africa referred to as the "Dark Continent"?

During the middle of the 19th century, Africa was referred to as the "Dark Continent," because little was known about the mysterious land itself. The term "Dark Continent" was most likely used for the first time by United States explorer and journalist Henry Stanley.

While it is well known that the African continent was mostly under European control until the late 19th century, it was still hardly mapped out and explored, even after the European powers divided the land among themselves. It was not until the 20th century that those people occupying Africa were able to further explore the land and take full advantage of its abundant resources.