It is said that long ago, before Glastrier was born, the Crown Tundra was called the Crown Region and fit for human habitation. The winters were long, but enough crops grew to almost support the population, most of whom supplemented their diet with fishing along the region's long coastline.
And then the world froze. Driven by the promise of carrots, the crystal horse Glastrier raided the granaries and trampled the fields, turning the land into permafrost. Kings tried in vain to tame it, and most of them died in the attempt – but they saw no alternative, for even before it was ever done, the people of the Crown Tundra held that only one who tamed Glastrier was worthy of the kingship.
Most of the Tundra's population had already fled to warmer climates, and its few remaning people were debating between declaring a republic and abandoning the region as refugees, by the time that Calyrex declared its candidacy. I need not recount here the legend of how it tamed Glastrier with its own icicles, and the controversy over the identity of Calyrex's mount is a story for another day.
Suffice it to say that enough of the ice melted away that the region enjoyed centuries of prosperity, that the people warmed to Glastrier, embracing this pokemon as a symbol of the region's harsh yet survival climate. And despite the parallels to the age when it arrived, it is difficult to imagine how Glastrier could possibly be responsible for the Crown Tundra's ultimate sad fate.