Answer:
widespread diseases such as malaria and sleeping sickness
Explanation:
Geographic barrier refers to a form of hindrance that is caused by the natural topography and location of a place. Diseases do not fit this definition.
In the past, medical knowledge hasn't been as developed as it is today. Because of this, many sickness that we considered as mild actually very deadly by the people at that time.
Even until today, African continents is the home of more than 90% case of malaria worldwide. At that time, many European traders warned one another about this disease. This made a lot of them choose to avoid Africa as trading destinations. They did not wanted to bring the disease back home since they had no idea how to handle it.
