There were really just separate groups that were celebrating soldiers for various reasons.  One of the most prominent contributors to the modern day Memorial Day seems to be General John A. Logan, who called for a “Decoration Day”.  As feminine as that sounds, the flowers were going on the graves of fallen soldiers.  He specifically chose May 30th for the date, as that was not the day of any significant battle.  That was well over a hundred years ago, but the holiday hasn’t evolved that much, all things considered.

Side note: That was initially supposed to be a flag hat on Chinny’s head.  It instead looks like it’s coming from within his head.  I kept it because it looked like his only thought was “America!”