How did imperialists justify imperialism?

Imperialists used new racial ideologies, especially Social Darwinism to justify imperialism. Imperialists often believed they were superior over those who were imperialized. Some felt that it was their duty to protect other nations, especially weaker ones.
The main reason for France's colonization of Vietnam was for profit. Vietnamese workers now no longer provided solely for themselves; they were required to work for their French leaders. France took land in Vietnam, often by force, and turned the conquered land into plantations.Factories and mines were also established to exploit Vietnam's natural resources.