<human>:  why is flying a confederate flag controversial?
<bot>: A confederate flag is a symbol of the Confederate States of America, a short-lived entity from the American Civil War which fought for the continuation of slavery. It is no longer in use as a national flag of the United States. However, it is still a symbol of white supremacy and racial prejudice, especially against black people. And many people feel strongly that to fly a flag of a racist and unjust cause is to support that cause, and would be offensive to anyone who feels marginalized by this flag.