The First Balkan War

The First Balkan War pitted Russia, Rumania, Montenegro and Servia against the Ottoman Empire in what was to be the first of several wars over the division of the Balkan region. The war began when Servia was found to have given aid to a Bulgarian rebellion inside Ottoman territory, which prompted the Porte to invade Servia and the Russians to declare war in response. Though the Turkish forces fought well, and at several times appeared to be winning the war, after fourteen months the Russians were on the Maritsa and the British forced the Ottomans to call a truce before Constantinople fell into enemy hands.

(This is from SoaP, BTW)