Diseases helped colonized Americas but saved Africa in a way.
“Rates of disease mortality among European soldiers stationed at the relatively less malarial port-and-fort posts they maintained (which we’ve discussed in this series) in the period period to the Scramble could still exceed 60%, often substantially so. While disease was almost always in the pre-modern world more of a killer than actual combat, rates of attrition that high created an effective disease wall which could swallow effectively unlimited European armies whole. “
https://acoup.blog/2021/09/03/collections-teaching-paradox-victoria-ii-part-iii-worlds-fair/