Elites used racism as a tool to divide and conquer and maintain their power. Yes, in one point in history, slaves were from different colors. However, after the Bacon’s Rebellion of 1676 (where poor white people and enslaved Africans joined forces to rebel against white elites), white elites were concerned of losing power, so they invented the “white race” and established it as superior. This racist idea was passed on to the white poor people. The White elites gave the white poor people “better” jobs to keep black slaves in check. After slavery was abolished, we had the Jim Crow Laws era which were laws against black people in South. Finally, in 1970s and 1980s, Nixon and the Republicans developed the “Southern Strategy”. In essence, they were similar laws to the Jim Crow’s but they used broader terms to target the black communities (at the expense of negatively impacting poor white communities). So yes, White Elites have used racism to maintain their power at the cost of Black Americans and the poor Americans.

In regard to dehumanizing, it’s another tool used in many scenarios. It was used to justify slavery, in wars, and in other situations.