In 1898, African-Americans in Baltimore demanded that the city’s all-white police force hire black officers. The police commissioner issued a curt reply: no. Employing “colored policemen” would result in the “humiliation of Anglo-Saxon blood,” he warned, especially if a black officer were to arrest a white citizen. Baltimore didn’t hire its first black policeman until 1938.

I’ve been thinking about this history during the recent crisis in Baltimore, where six police officers have been charged in the death of Freddie Gray. Three of them are black, leading some observers to contend that the killing of Gray — who was also African-American — was “not about race.”

But when it comes to urban policing, everything is about race. And nobody understands that better than African-American police officers, who have faced brutal discrimination across our past. As we seek justice for Freddie Gray, then, we also need to ensure just treatment of the accused black officers.

Before the Civil War, whites-only police forces helped maintain slavery by arresting black runaways. During Reconstruction, a few Southern cities started to hire black police, triggering white outrage.

In New Orleans, critics worried that an “Africanized” police force would not defend laws that segregated blacks on streetcars. In Vicksburg, Miss., seven recently hired black officers were forced to resign after whites protested. “Law enforcement means domination,” one politician explained, “and the white man is not used to being dominated by Negroes.” ...