But what if WW1 didn't start in 1914,either due to Franz Ferdinard not getting shot or cooler heads prevailing? What if Romania does declare war on Bulgaria that year? Does it end Bulgaria being a military threat for Romania or will the same thing that happened OTL happen here as well,with Bulgaria being more angry and resentful to Romania? And would the Great Powers intervene in any way or will they remain neutral like in the Second Balkan War?
OK - so what we need to have happen is Franz Ferdinand survives his visit to Sarajevo on St. Vitus Day 'For Want of a Sandwich' style. Or he is smart enough to avoid Bosnia on St. Vitus Day. Or better yet, to keep Austria-Hungary as similar as possible to OTL, he does not get assassinated in Sarajevo on St. Vitus day, but on drive in the hilly roads of Bosnia or Croatia soon after his visit, his driver loses control over the car and he perishes in a car accident. It is ruled accidental however, with no foul play suspected.
In any case this divergence or divergences all happen by the end of June or early July. And they *don't* butterfly away this lethal incident with the borderguards in Romania and Bulgaria later on in July.
Romanians are angry about this incident started by the Bulgarians, the Bulgarians are angry about the murder/lynching of their guards after they were disarmed. The Romanians decide to go to war with Bulgaria.
What do the Romanians want? The Romanians actually have about as much land, even more, than they want from the Bulgarians, and probably don't want to acquire more land with more Bulgarian and Turkish speakers. But maybe they are figuring the incident is a symptom of Bulgarian vengefulness and aggressive attitude that needs to be slapped down hard before it worsens or Bulgaria recovers anymore from its 1913 defeat, so Bulgaria needs a good kick to stay down. And maybe Romania can force an indemnity from Bulgaria and dismantle some fortresses. Maybe the Romanians assume their 2nd Balkan War allies will be happy to jump in.
If Bucharest DoWs Bulgaria, and invites Constantinople, Athens, and Belgrade to join in the beat down, I don't think Constantinople would be that interested. They were more concerned with Greece on the Aegean, and were nearing an alliance with the Bulgarians.
Athens was more worried about losing their naval advantage with the arrival of the Ottoman dreadnought, and was contemplating attack on the Ottoman fleet and Constantinople to force mediation to ratify its ownership of occupied Aegean islands. Bucharest could try to sell the Greeks on the opportunity to annex Bulgaria's Aegean coast, but that wasn't Athens' priority at this point. Athens' hope vis-a-vis Bulgaria was that it *not* side with Turkey and that it possibly side with Greece to strengthen Greece's odds.
Serbia probably had all it wanted from Bulgaria in terms of control over Vardar Macedonia and a favorable border. Serbia's prime concern was protecting itself from Austria-Hungary, unifying with Montenegro, and undermining Austro-Hungarian control of Bosnia and other South Slavic lands.
Now Bulgaria won't exactly have many champions either, especially not from Romania. In Austria-Hungary, I suspect the Magyars would have their usual schizophrenia about things - they wouldn't want the Romanians to win or be strengthened, indeed they'd prefer them to be crushed, because of their claims on Hungarian Transylvania. But at the same time, the Magyars wouldn't want to absorb any territory with ethnic Romanians on it. Their ideal fantasy solution would be if the Black Sea just flooded Wallachia and Moldavia. Magyars would sympathize with Bulgaria and probably so would Conrad, who would advocate war on Romania to save Bulgaria, despite the Romanian alliance. If alive, Franz Ferdinand would be against the idea of war. Others in Austria might sympathize with Bulgaria, but would see Serbia as a higher priority threat and still find it impossible to see Romania as an enemy because of the remaining formal secret alliance with the Romanian King.
The Germans, still hopeful about alignment with Romania, would probably be against any action against Romania on behalf of Bulgaria.
I don't think that Russia would act like a protective big Slavic brother on Bulgaria's behalf and move against Romania to protect Bulgaria, given the number of recent and historic disputes with Tsar Ferdinand
Turkey may see utility for Bulgaria as an ally against Greece in an impending conflict, but has no use for a conflict with Romania.
So, for the moment, if Romania is proceeding to attack Bulgaria, things seems set to leave it a one-on-one war, until additional developments, on the battlefield or off, press other powers to intervene.
Am I personally missing a motive for Austria-Hungary, possibly with German support, to join in on Romania's side *against* Bulgaria, honoring the secret alliance with King Carol? That seems pretty wild and out there to me.
Personally, I could imagine the Russians intervening on the Romanian side against Bulgaria, with the idea of splitting the occupation so that Romania occupies the north and west, and Russia reestablishes the principality of Eastern Rumelia in an occupation zone covering southern and eastern Bulgaria. This would wrap Russian military control around Turkish Thrace and the straits, establish a shore base on the Aegean, and permanently block any prospective Bulgarian or Greek landward routes of advance to Constantinople, while putting Russia in a position to make such an advance at a convenient later time.
Of course I don't see that as especially likely, just a wildcard more dictated by the rule of cool.
What does anybody else see happening if Romania makes a move and there is a one-on-one fight, or if some other powers cannot keep their hands off the situation?