Sweden didn't use to have one either because there is no single day that is more suitable than any other day.
The day commemorates the invasion of Europe at Normandy?
We have no national day.
Even Liberation day is not a reason to have the day off, most of the years. The Netherlands want to give up all, for economy. Next year we will have the day of on the fifth of may, because then it is a 70th anniversary.
Get one.
As you may know, we have July 4, which commemorates the Declaration of Independence. We have other national holidays commemorating various events (Veterans Day, Memorial Day), but July 4 is Independence Day.