In the past week Americans marked the anniversaries of two major events that hold different places in the common memory. One evoked feelings of honor and pride, the other shame and revulsion. June 6 was the 77th anniversary of the D-Day invasion; May 31 was the centenary of the Tulsa race massacre, one of the most violent acts of domestic terrorism in U.S. history. But unlike D-Day, the Tulsa massacre had been largely forgotten until recent efforts succeeded in drawing attention to its relevance in a nation still grappling with a legacy of racial injustice. Northwestern University historian Leslie Harris explains why it is so difficult for Americans to reckon with the darkest chapters of our past.