An often very annoying alternate history cliché.
When an author or map-maker pushes the Balkanize Now button on any nation because it looks good on a map, they have a grudge against that country or can't be bothered to come up with anything else to do with that nation.
Especially wrong with culturally and ethnically homogeneous nations in which secessionist urges did not exist, such as England, Spain (post-unification, borderline case to be fair), Japan, etc. The two Koreas and two Germanies are real historical examples of more random-looking balkanization.