Why was the Balkan League formed? O To rival the power of the Ottoman Empire
O To plan the assassination of Archduke Ferdinand
O To create an alliance to rival the Central Powers
O To plan an attack against Russia

Correct answer is To rival the power of the Ottoman Empire.

Explanation:

First option is correct as it was an alliance created to throw out Ottomans from the Balkan Peninsula, as they were reigning in some territories that the Balkan nations believed were their.

Second option is not correct as this refers more to Triple Entente.

Third option is not correct as organization that planned his assassination was Black Hand.

Last option is not correct as most of the members of Balkan League were Russia's allies.