Allied Army of the Orient

When Germany, Austria-Hungary, and the newly joined ally, Bulgaria, were about to overrun Serbia in September–October 1915, the returning multi-national troops from the failed Gallipoli campaign disembarked in the Greek port of Salonika to establish the Macedonian Front.

A side-effect of the landing was the further burdening of the National Schism between Constantine I of Greece and the Prime Minister Eleftherios Venizelos, ending in the forced resignation of the latter.

After a coup on 30 August 1916, the Provisional Government of National Defence, led by Eleftherios Venizelos, was created in Salonika.

In June 1917, after increasing pressure from the allies, King Constantine I of Greece was forced to abdicate from the throne.

Venizelos assumed control of the entire country and Greece officially declared war against the Central Powers on 30 June 1917.

Allied collaboration: an Italian captain, a Russian lieutenant, a Serb colonel, a French lieutenant, and a Greek gendarme
Serbian Field Marshal Živojin Mišić and British General George Milne
Sarrail and Petitti di Roreto on the arrival of the Italian troops in Salonika
General Gérôme and Venizelos inspect Greek troops in Macedonia