How did imperialism become associated with social darwinism

Social Darwinism was a sociological theory popular in late nineteenth-century Europe and the United States. It merged Charles Darwin's theory of natural selection and Herbert Spencer's sociological theories to justify imperialism, racism, and laissez-faire (i.e. conservative) social and economic policies.

the decreasing neutrality of the u. s. in world war i

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the second significant cause of the great migration was the desire of black southerners to escape segregation, known euphemistically as jim crow. rural african american southerners believed that segregation - and racism and prejudice against blacks - was significantly less intense in the north.