The majority of American adults believe that more than 150 years after the 13th Amendment ended slavery in the country, the legacy of slavery still affects how black people are treated in modern American culture. According to a recent Pew Research Center study, more than four out of ten respondents believe that racial equality has not been sufficiently advanced in the country. There is also some doubt that black people will ever enjoy equal rights with white people.
It is in the human nature to fear, despise and dislike anything considered "different", but it is also in our nature to mature and be rational about these instincts. It is not just racism, but also different cultures, religions or ways of thinking.
So, racism has not "come", it is something that humans just have by default, so unless you become aware of this, it will be there in all your decisions. Part of becoming adult is deciding what is right and wrong in our own nature, so most people will decide that racism, while quite natural, is undesirable and avoid racist attitudes. In people who are at a more mature level, racism as such dissapears.