I put this in Post-1900 mainly because I'm sort of wondering if a more desperate Bulgaria might accept a union with Serbia under any circumstances (I sort of recall this being floated as an out there idea to avoid territorial losses after the armistice?) but it could easily apply to pre-1900 as well, so this is sort of arbitrary.
Something I've sort of always wondered is whether there was any sort of "Pan Slavism" in Bulgaria, since from an outsider's perspective Serbia's hankering after the Habsburg provinces was rather... odd. (Nationalists gonna nationalist I guess). Historically speaking Serbia and Bulgaria have trended much more towards the Byzantine (and Ottoman) side of things while Croatia and Slovenia were always part of the "western" ie Roman/Latin/German/Catholic side of things, and IIRC the historical Serbian Empires tended to push south through Macedonia, Albania and parts of Greece rather than north (albeit I think parts of Bosnia were part of Dusan's empire?).
So I guess I'm wondering if it would be at all plausible for a Serbo-Bulgarian union to form an alternate "Yugoslavia" and what such a nation would look like in practice. At a guess I'd say somewhat strengthening the Ottomans so that Serbia and Bulgaria have a longer history of being Turkish provinces, and end up revolting together- perhaps with a single (Romanov?) prince installed as a consequence of some war or another. Presumably this state would focus much more on expanding south, into Thessaly, Albania and Thrace, though gunning for Montenegro, or parts of Bosnia or Austria Hungary are hardly implausible..
Something I've sort of always wondered is whether there was any sort of "Pan Slavism" in Bulgaria, since from an outsider's perspective Serbia's hankering after the Habsburg provinces was rather... odd. (Nationalists gonna nationalist I guess). Historically speaking Serbia and Bulgaria have trended much more towards the Byzantine (and Ottoman) side of things while Croatia and Slovenia were always part of the "western" ie Roman/Latin/German/Catholic side of things, and IIRC the historical Serbian Empires tended to push south through Macedonia, Albania and parts of Greece rather than north (albeit I think parts of Bosnia were part of Dusan's empire?).
So I guess I'm wondering if it would be at all plausible for a Serbo-Bulgarian union to form an alternate "Yugoslavia" and what such a nation would look like in practice. At a guess I'd say somewhat strengthening the Ottomans so that Serbia and Bulgaria have a longer history of being Turkish provinces, and end up revolting together- perhaps with a single (Romanov?) prince installed as a consequence of some war or another. Presumably this state would focus much more on expanding south, into Thessaly, Albania and Thrace, though gunning for Montenegro, or parts of Bosnia or Austria Hungary are hardly implausible..