Memorial Day originated after the U. S. Civil War as Decoration Day.
At the opening of summer, people would mark this by decorating the gravestones of the war dead. The Victorian Era, of course, had a particular relationship to death. Co-incident with this was the popularity of cemeteries. Brooklyn's Greenwood Cemetary rivaled Central Park's popularity for Sunday pinickers after Vaux & Olmstead's Manhattan oasis opened in 1873.
Back to the Civil War for Decoration Day, a blog repeat: