Arab Nationalism
While in the Balkans the Russians were helping the Greeks, the Serbs and the Bulgarians to attack the Ottoman Empire and annex her territories, in order to prevent the Germans from connecting to the Ottoman Empire through the Baghdad railway, and in order to gain control of Constantinople, the English were organizing an Arab revolt against the Ottomans.
The English were organizing the Arabs at the Southern parts of the Ottoman Empire, the regions that today are Saudi Arabia, Iraq and Syria, in order to push the Ottomans away from the Persian Gulf.
Therefore we see that the allies were helping the local populations both at the Balkans and in the Arab world, in order to turn them against the Ottomans and prevent Germany to connect to the Persian Gulf through the Baghdad railway. For the Arab revolt, 1916-1918, see the following Wikipedia link.
https://en.wikipedia.org/wiki/Arab_Revolt
Therefore by supporting Balkan Nationalism, the allies managed to block the connection between the German and Ottoman Empires (black line), and at the same time, by supporting Arab nationalism in Syria and Iraq, they managed to block the connection between the Ottoman Empire and the Persian gulf (red line).
