At the request of the Greek prime minister, Eleutherios Venizelos, Britain and France agree on October 5, 1915, to land troops at the city of Salonika (now Thessaloniki), in northern Greece, during World War I.
Earlier in the war, David Lloyd George, Britain’s minister of munitions, had argued for sending Allied troops to Salonika instead of the Gallipoli Peninsula; the idea was shelved when the ill-fated invasion of Gallipoli went ahead in the late spring of 1915. In early October of that year, however, Britain and France each agreed to contribute 75,000 troops to establish a base of operations in Salonika, from which they would attempt to aid their battered ally in the Balkans, Serbia, in its struggle against the Central Powers.
The expedition had three major drawbacks, however: First, it would conflict with the demands of Gallipoli operation, which was ongoing but locked in a virtual stalemate. Second, such a large Allied force could not be fully established in Salonika until the following January, which would undoubtedly be too late to aid the Serbs. Finally, such an operation would violate the neutrality of Greece. Though many in that country, including Venizelos, favored intervention in the war on the side of the Allies, King Constantine remained steadfastly neutral; married to a relative of Kaiser Wilhelm II, his natural sympathies lay with Germany. Lloyd George, for one, dismissed the idea of a violation of Greek neutrality, arguing disingenuously that "there was no comparison between going through Greece and the German passage through Belgium." In fact, a goal of the Salonika expedition, expressed by Lord H.H. Kitchener, the British secretary of war, was to provoke Greece into intervening and aiding Serbia against the Central Powers.
Another objective of the operation in October 1915 was to defend Greece against invaders from Bulgaria, which entered the war that same month on the side of the Central Powers. In the end, however, the Anglo-French force began arriving too late to aid the Serbs—the Serbian capital, Belgrade, was evacuated and occupied by the enemy on October 9—and was not strong enough for an aggressive offensive against the Bulgarian invaders. Against the objections of Constantine and his supporters, the Allies remained in Salonika, as yet another front in World War I became bogged down in stalemate over the course of the next year.