... and named Decoration Day.. became a legal holiday (the last Monday in may; in most states) in memory of the dead servicemen...

Decoration Day: in Southern states, Confederate Memorial Day is variously observed on April 26,
may 10, June 3, etc....

Changed after WWI (Memorial Day)... to include all US Service persons who died in all wars.

Just found this in Webster's New World Dictionary of the American Language.