Answer: They believed that their economy would collapse under European rule.
One of the main reasons why Africans resisted to European imperialism was due to their interest in protecting their economic interests. Many of the initial conflicts between the two regions were due to trading partnerships. The treaties that were signed were considered by Europe as a recognition of their superiority, while for Africans they were simply commercial treaties. Africans resisted this interpretation, as they wanted to remain full-fledged actors. Moreover, as trade intensified, Europeans were more and more interested in implementing some kind of "free trade" for their benefit. Africans believed this would not only put them in a disadvantaged position, but it could cause their whole economy to collapse.