It's been nearly 200 years since white performers first started painting their faces black to mock enslaved Africans in minstrel shows across the United States. It was racist and offensive then, and still is today.

The latest controversy to erupt over blackface is a photo in Virginia Gov. Ralph Northam's medical school yearbook. It depicts one person in blackface and another dressed as a member of the Ku Klux Klan. After initially apologizing for appearing in the photo, the Democratic governor now says he is neither the person in blackface nor the person dressed as a Klansman.

However Northam's case plays out, it's important for every American to understand what blackface is and why it's so offensive.