Racial issues in The United States? What causes racism?

Racial issues, known about or not, are sadly somewhat common in the US. I won't say which races against one another to prevent any implications. The cause of racism? More than half of the time, the belief that one race is superior or greater than another or all others. The most known example of this was when before slavery & segregation was abolished in the United States, African Americans and all other minorities were viewed as second class citizens in favor of white people. It is either the ideaology of false-superiority or negative bias due to ignorance, fear, or previous experiences.