Arthurian for England. Imagine Merlin and Churchill. The dialogue would be beyond amazing.

The United States would have Superheroes methinks. Thunderbirds are nice, but they are more symbolic of Native Americans.

Cthulhu, though imagined by an American, would best suit Japan. Cthulhu looms deep and distant in the Pacific, after all. And there are comparisons to Godzilla. 

This is nice and all, but now you have to tie it all together to be something coherent.