Although the Portuguese arrived on Cameroon's doorstep in the 16th century, malaria prevented significant European settlement and conquest of the interior until the late 1870s, when large supplies of the malaria suppressant quinine became available. The early European presence in Cameroon was primarily devoted to coastal trade and the acquisition of slaves. The northern part of the country was an important part of the Muslim slave trade network. The trade was largely suppressed by the mid-19th century. Christian missionaries established a presence in the late 19th century and continue to play a role in Cameroonian life.