How did Herbert Spencer hijack Charles Darwin's theory of evolution and natural selection?

Herbert Spencer appropriated Charles Darwin's theory of evolution by coining the phrase "survival of the fittest," which he used to promote his own social and political ideas, particularly in the context of social Darwinism. While Darwin focused on biological processes, Spencer applied evolutionary concepts to society, arguing that competition among individuals and groups justified social inequality and laissez-faire capitalism. This misapplication often distorted Darwin's original ideas, leading to misconceptions about natural selection and its implications for human behavior and societal structures.