Samuel Battle’s first three attempts to become a police officer were rejected because he allegedly had a heart murmur. Before his fourth attempt, Battle went to an independent doctor, and, in 1911, after receiving a clean bill of health, he became the first black officer appointed to the metropolitan New York City Police Department. Battle was stationed in the West Sixty-eighth Street precinct. Almost fifty years after he joined the force, he participated in a Columbia University oral-history project. Battle communicated an impression of strength. He was a big guy—six feet three inches, two hundred and eighty-five pounds—and his personality seems to reflect that, especially when he tells one story about how he was treated at the precinct.

They never made any threats personally, to me. Never. Nobody would ever do that. But there was one occasion, when I was at the flag loft—and this was before Sergeant Stewart came up there to stay with me—I found a note pinned right over my bed, with a hole in it about the size of a bullet hole. It could have been done; I don’t think they shot off a gun, but it was something to make it look like a bullet hole. And on this note was written: “Nigger, if you don’t quit, this is what will happen to you.”

On the day he was appointed, Battle said, Rhinelander Waldo, who was then the commissioner, told him, “You will have some difficulties, but I know you will overcome them.” Perhaps his reaction to the note fulfilled that premonition: “After this note was left there, it didn’t faze me at all,” he said. “I didn’t care; it didn’t make any difference. I knew whoever did it was a coward.”

Battle also recalled a riot, in 1919, at 135th Street and Lenox Avenue in Harlem, where, he said, “The white officers worked in an all-Negro neighborhood, practically, and they needed me as much as I needed them, and sometimes more.” He was promoted to sergeant in 1926, and to lieutenant in 1935. In 1941, he became New York City’s first black parole commissioner. In 2009, the intersection at 135th and Lenox was named Samuel J. Battle Plaza.

Battle became an officer at a time when integration seemed to be the prevailing solution for what was then called the “race problem.” Police departments are not only institutions that aim to insure public safety; departments, and their unions, are powerful political machines, and in politics representation is important. But efforts to integrate police departments, however successful, have not erased tensions between police departments and black communities.

The origins of American policing, the historian W. Marvin Dulaney argues, cannot be fully understood without considering slavery and racism. “By the beginning of the eighteenth century, most American colonies had enacted laws to regulate the behavior of African slaves,” Dulaney writes in his book “Black Police in America.” “The codes also established the slave patrol or ‘patterollers.’ The slave patrol was the first distinctively American police system, and it set the pattern of policing that Americans of African descent would experience throughout their history in America.”

In the middle of the nineteenth century, as abolitionist movements gained momentum, the policing of black Americans—both free and enslaved—intensified. The Fugitive Slave Act of 1850 authorized federal agents to help find, detain, and return escaped persons to slavery, and required citizens to assist in the recovery. Moreover, the act stipulated, “In no trial or hearing under this act shall the testimony of such alleged fugitive be admitted in evidence.” The groups of white men that had constituted slave patrols a century before evolved into official, protected actors of the state, incentivized to use force to insure the existence of slavery. By passing the law, Congress made a moral calculation. Congressional leaders wanted to avoid a civil war. To that end, California entered the union as a free state, and the slave trade ended in Washington, D.C. Western territories could become slave states by popular vote. And, by way of the Fugitive Slave Act, the free parts of the country would police African-Americans in ways that foreshadowed the tragedies that would befall Eric Garner, Michael Brown, Walter Scott, and many others.

During this period, some African-Americans also became police officers. “By accepting the racial status quo and the legal oppression of other blacks, these law enforcement officers became the first African Americans to confront the paradox of policing a society where the color of a person’s skin often determined guilt or innocence,” Dulaney writes. “They also became the first to accept such roles because they believed that they could improve their own precarious position in a society where status was based on skin color.”

Since Trayvon Martin’s death in February, 2012, Americans have been discussing the relationship between young black men and law enforcement with new intensity. The Dream Defenders, the Ferguson protests, the #blacklivesmatter hashtag, and other social-justice efforts make it difficult for anyone to ignore the hostility between police departments and black men and women. In the past three years, we have become familiar with a long list of names, including Rekia Boyd, Kimani Gray, Garner, Brown, Akai Gurley, Tamir Rice, Scott, and Freddie Gray. As demonstrated in the Department of Justice’s report on Ferguson, the killings tell only part of the story. “Our investigation has shown that distrust of the Ferguson Police Department is longstanding and largely attributable to Ferguson’s approach to law enforcement,” the report states. “This approach results in patterns of unnecessarily aggressive and at times unlawful policing; reinforces the harm of discriminatory stereotypes; discourages a culture of accountability; and neglects community engagement.”

In New York City, things came to a breaking point this past December, when two N.Y.P.D. officers, Rafael Ramos and Wenjian Liu, were killed by a man who, at least according to his social-media postings, was seeking revenge for the deaths of Garner and Brown. In the last days of 2014, Mayor Bill de Blasio gathered with Governor Andrew Cuomo, Vice-President Joseph Biden, and others to pay tribute to officers Ramos and Liu. At the funeral for Ramos, as the mayor rose to speak, many of the police officers watching on screens outside of the church turned their backs to his image in dissent. In the opinion of many of the officers, de Blasio had fanned public discontent with the N.Y.P.D. by making statements that month about how he had warned his son, Dante, to be careful when engaging with police officers. “Look, if a police officer stops you, do everything he tells you to do. Don’t move suddenly, don’t reach for your cell phone,” de Blasio said he told his son. “Because we knew, sadly, there’s a greater chance it might be misinterpreted if it was a young man of color.”