I got curious about various things about official recognition of national sovereignty, which quickly led me to Wikipedia's List of unrecognized countries.
There's all sorts of fiction fodder there. Walter Jon Williams already did a lot with this general idea, by featuring Transnistria prominently in his novella "The Green Leopard Plague," but I think there's plenty more that could be done.
I especially like the names "South Ossetia" and "Nagorno-Karabakh" in the modern sections. But the historical section is mostly what I wanted to point to, full of evocative names and material for alternate-history stories: Finnish Socialist Workers' Republic; Free and Independent Republic of West Florida; State of Muskogee; Bougainville; Lajtabansag State; etc.
I'm not really sure what that page's distinction is between a historical unrecognized state and a historical failed state; it seems to me that states and quasi-states have to exist for a certain amount of time before you can really call them "unrecognized." So if they're going to include Lajtabansag State, which lasted for 32 days in 1921, there are probably a lot of other statelike entities they could list that didn't last long enough for anyone to decide whether to recognize them or not.
Anyway, thought it was an interesting list.