In 1919, the United States was roiled by the greatest wave of strikes in its history, as well as by fears that the radical appeal of the Russian Revolution might spread across the Atlantic. The country was also in the grip of rising hostility toward immigrants, inflamed further by paranoia that these newcomers were bringing socialist and anarchist sympathies with them from Europe.

Early that year, the US Army’s domestic Military Intelligence Corps, which deployed hundreds of agents during World War I and its aftermath to spy on Americans, produced an unusual map of much of New York City.

It divided the city into zones of eleven different colors, highlighting which dangerous ethnic group lived where: red for “Russian Jews,” orange for Italians, green for Irish, black for “Negro.” The map was also sprinkled with numbered blue stars and white circles. The eighty-six circles marked the locations of union headquarters, IWW halls, and other places “where radical meetings are held,” while the forty-four blue stars identified offices of “radical and liberal” publications, from the Intercollegiate Socialist to the literary and political journal the Dial and the NAACP’s the Crisis.