A day to reflect — as some try to forgetManhattan: Juneteenth marks the day in 1865 when Union troops arrived in Galveston, Texas, to ensure that all previously enslaved people were aware of their new freedom, two years after the Emancipation Proclamation was signed by President Abraham Lincoln. The commemoration this year highlights a trend toward a chilling erasure of history, culture and achievements of African-Americans. This signals a perilous course for all Americans. Ironically, one of the more blatant occurrences of an attempt to purge Black history took place in one of the “bastions of freedom,” Philadelphia. An exhibit...