For me, the event would be the Supreme Court decision in Loving v. Virginia. That decision made it unconstitutional for any state to ban interracial marriage.
In 1967, when this case was decided, my parents were already in an interracial marriage. Only 16 states banned such marriages. However, such laws were still legal and they helped to create an atmosphere in which racism was acceptable and there was a presumption that people should marry within their own race.
Nowadays, there is no such presumption. I am half-white but don't look it. I'm married to a white woman. No one has ever said anything to me about it in any part of the US. I do not think that this would be the case if Loving had not been decided as it was.