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Let's say that at the end of World War 1, there is no Yugoslavia and Serbia doesn't get Slovenia or Croatia. Maybe this is because the Entente decides that Yugoslavia is a bad idea and Croatia should be independent, or Austria-Hungary has a separate peace earlier in the war and somehow manages to stick together and becomes Trialist. The PoD isn't the main issue here. The question is: How would Bosnia and Herzegovina be divided between the Serbs and Croats? Let's assume that the Entente gives some weight to the notion of self-determination, but also values nice borders, balance of power, and geopolitics. Let's also assume that while the Entente ideally wants borders that will promote longstanding peace and stability without provoking Croat irredentism, it leans in favor of the Serbs; the Entente also doesn't care much what Muslim Bosniaks want. How would the border being Greater Serbia and the Croat state be drawn? Serbia is still uniting with Montenegro it doesn't need to get coastal access from Bosnia and Herzegovina, but would still appreciate it anyways.
I've attached the following two maps. The first is a geographic map of Bosnia and Herzegovina, the second is an administrative map of Bosnia and Herzegovina while it was under A-H rule. The borders of the A-H administrative units were copied from the Ottomans. The bold black lines represent kreise, the lighter grey lines represent bezirke. It seems that the southern part of the Mostar kreise became part of SR Croatia and independent Croatia OTL, but that doesn't necessarily have to happen TTL.