Tensions in the United States reflect a 69 year-old question: what happens when the American promise fails? — The streets of Harlem, New York were thick with tectonic tension when Langston Hughes wrote of a “dream deferred” in 1951. A city — only 13 miles wide — was divided, seemingly irreparably. Although more visible than the economic inequity of Dickens’ Britain, Manhattan, too, told a tale of two…