Croatia has German troops in it. The Serbs made their intentions to form Yugoslavia public right before invading Bosnia. Croatia (which also includes Slovenia) contacted Prussia (which includes Austria, their former overlords) and asked for help. In exchange for access to their ports on the Mediterranean (in which Prussian warships will likely be stationed), Prussia agreed to send a small but significant force to Croatia to act as a deterrent to Serbian aggression. 

So expect some Germans guarding your borders and stumbling around your ports, probably stealing your women.