Memorial Day, which originated as Decoration Day, originally honored only those lost while fighting in the Civil War. During World War I, the holiday evolved to commemorate American military personnel who died in all wars and expanded into a day of remembrance for loved ones and fallen soldiers. In 1968, Congress passed the Uniform Monday Holiday Act, which established Memorial Day as the last Monday in May in order to create a three-day weekend for federal employees. The change went into effect in 1971. The same law also declared Memorial Day a federal holiday.

Some people wear a red poppy in...