A.) American imperialism
B.) American slavery
C.) unplanned deaths of Native Americans caused by disease
D.) unplanned deaths of settlers from conflicts.
You didn't give any choices but if these, then the correct answer of this question is option A. The dark side revealed by Manifest Destiny is the American imperialism. It is the belief that American settles are destined to expand across North America. This resulted to displacement of Native Americans and war with Mexico