I'm sure there's a word for this, but I don't know what it is. Specifically, the concept associated with nationalism - the glorification of a past time period as being better than the current one, which usually results in exaggerating that time period's positive aspects and downplaying its negative aspects. It's not quite nostalgia, I don't think.
Two words I often use when I'm doing that myself are:
- romanticizing: transitive verb : to make romantic : treat as idealized or heroic intransitive verb 1 : to hold romantic ideas 2 : to present details, incidents, or people in a romantic way
- glorifying: transitive verb 1 a : to make glorious by bestowing honor, praise, or admiration b : to elevate to celestial glory 2 : to light up brilliantly 3 a : to represent as glorious : extol b : to cause to be or seem to be better than the actual condition
Try saudade, a Portuguese word I just learned about this year. It is a nostalgic longing for a past or a place or something that has happened, or maybe hasn't, but tinged with distinct melancholy and a sense of loss.
Saudade — ODO
noun (Especially with reference to songs or poetry) a feeling of longing, melancholy, or nostalgia that is supposedly characteristic of the Portuguese or Brazilian temperament
"her songs are based on love poems and evoke a melancholy known to the Portuguese as saudade"
People often refer to the Myth of the Golden Age for this kind of delusion. The term "The Golden Age" originally referred to a posited era of extreme wealth and prosperity in Greek mythology. However, nowadays it's often used in relation to crime, sociology, politics and many other areas to describe a supposed golden period which never actually existed, but is always cited by humbugging reactionaries.
An excerpt from STREET DISORDER IN THE METROPOLIS, 1905-39 Stefan Slater:
When all is said and done, our perceptions of violence do indeed depend on where we look. That, if nothing else, should alert us to the possibility that, in our eagerness to dispel the myth of a conflict-free golden age, we may be exaggerating the tensions of [earlier societies] while overlooking the reality of violence in our own times.
A sub-title in a California Law Review paper: Right to Marry, Martha C Nussbaum:
MARRIAGE IN HISTORY: THE MYTH OF THE GOLDEN AGE
The popular myth of a golden age of urban recreation does not include the reality of white violence and black exclusion.
if it's England there's a term Merrie or Deep England: ""Merry England" is not a wholly consistent vision but rather a revisited England which Oxford folklorist Roy Judge described as "a world that has never actually existed, a visionary, mythical landscape, where it is difficult to take normal historical bearings."" from Wikipedia.