Austria-Hungary's slice of the spoils of 1878 was the province of Bosnia and Herzegovina. Taking it should have been straight forward, but the locals turned out to want to have a say in things. The result was a pretty obscure military campaign that is not particularly well known, but everything you probably need to know about the historical invasion is on the Wikipedia page.
https://en.wikipedia.org/wiki/Austro-Hungarian_campaign_in_Bosnia_and_Herzegovina_in_1878
Historically, the invasion started on 29 July 1878, after having been sanctioned by the Congress of Berlin. In this history the invasion will move forward by a month as Austro-Hungary would not want to risk their prize being taken away. They will need all of the 80,000 troops they would eventually assemble as even without Turkish intervention Bosnian guerrillas would give them a hard time.
Alas for wargamers wishing to depict Austrians in their wonderfully flamboyant white uniforms, they were no more. After being target practise for the Prussian needle guns in 1866 they had opted for a more subdued look. Not quite as drab as they were to appear in the Great War, but getting there.
There probably isn't much scope for massed battles on this front, but plenty of opportunities for small unit actions as Austrian regular troops face nimble guerrillas in forested mountains.
