Final answer:
The relations that were strained due to the wars in the Balkans were between Serbia and Austria-Hungary. Tensions were fueled by unresolved conflicts and territorial disputes.
Step-by-step explanation:
The relations that were strained due to the wars in the Balkans were between Serbia and Austria-Hungary. The tensions between these two countries were fueled by a history of unresolved conflicts and territorial disputes. The assassination of the Austro-Hungarian archduke by a Serbian nationalist led Austria-Hungary to declare war on Serbia, which eventually drew other countries into the conflict.