Racism is one of the most effective tools of oppressive power. The concept of 'race' was created in the 1700's by European scientists, who mostly based their practice on skulls. They went to the Caucasus Mountains, in western Asia/SE Europe (modern Chechnya) and measured skulls from this region, and compared them with other skulls from around the world. They found that skulls from the Caucasus region were larger, and decided that Caucasian people must be more intelligent than the other races: Negroid, Mongoloid, Malay, and American (Indigenous).This classification was explicitly and implicitly stratified - white people were at the top, with the most intelligence and virtue, and black people were at the bottom - this helped justify chattel slavery. Asian people were treated as the "next best" race after white, and so on. This hierarchy still exists, and is still manipulated for political purposes. For example, after the 9/11 WTC bombings, Arabic or Middle Eastern people went from being relatively high on this hierarchy to the being the lowest of the low.
This "science" was used to denigrate people of color and justify the colonialism, land theft, and slavery flourishing in this period of expanding capital.
Understand: race was created. There is no such thing as race, scientifically. Genetically speaking, an Inuit person may have more genes in common with a Bushman from southern Africa than with an American Indian or Sami person.
The definition of race that is often used in anti-racism organizing is this:
Race is a specious classification of human beings created at a certain point in history by Europeans who came to be called white, which assigns human worth and social status using "white" as the model of humanity and the height of human achievement for the purpose of establishing and maintaining privilege and power.
Note: the word "specious" means "false but appearing to be true."
This does not mean that race is not a social reality. It is a powerful idea that has been ingrained in us for 300-400 years, and it doesn't just disappear because it's based on a lie. Race has powerful and deadly consequences in the real world.
Everyone raised in this culture is exposed to race prejudice from a young age. It is practically impossible not to assimilate some of the racist stereotypes played out in this culture - an issue that plays out in many of us that is called internalized racism. At some level or another, all of us have internalized the lessons of race prejudice. Only by looking at these prejudices head on, analyzing what is behind them, addressing the role of power and hierarchy implicit in the race system, and working to dismantle this system at both personal and societal levels can we move forward.