Military. Many volunteers place American flags on the graves of military personnel and national cemeteries. Memorial Day is also considered the unofficial beginning of summer in the United States. In April of 1865, following Abraham Lincoln's assassination, commemorations were widespread. The more than 600,000 soldiers of both sides, north and south, who fought and died in the Civil War meant that burial and memorializations took on a new cultural significance. Under the leadership of women during the war, an increasingly formal practice of decorating graves had taken shape