Answer:
American imperialism
Step-by-step explanation:
Manifest Destiny offered feelings of ambition and self-confidence, quite similar to those that neo-colonialist ideologists at that time employed to explain the domination of regions in Africa and Asia. The manifest destiny preached American imperialism and favored the feeling that there were cultures inferior to American culture and that they should submit to the "superior" culture that was adopted in the United States.
Historically, Destiny Manifesto has justified the seizure of Mexican territories and the process of persecution and extermination of various indigenous communities. Externally, that same sense of gain and leadership was also one of the mainstays that explained US political and military intervention in other nations of the American continent.
With this we can conclude that the dark side of manifest destiny is American imperialism.