Struma Operation

The Struma Operation was an offensive operation by the Bulgarian army against the Entente, more specifically Greece and France, during the First World War. It was conducted alongside the Florina offensive. Its aim was to capture Greek territories in Eastern Macedonia. In 1016, Romania entered the Balkan War on the side of the Allied Powers. On the occasion of its entry, the Allied Powers planned a large-scale offensive campaign on the Macedonian Front. The Bulgarian High Command suspected an impending offensive, and the fighting that broke out around Doiran on 9 August merely confirmed these suspicions. The Bulgarians, for their part, pressed for an offensive in Macedonia, planning at that point to strike the two Allied flanks with the First and Second Armies. Meanwhile, on the western flank, the Chegan offensive led to the capture of Florina, but the First Army failed to capture Chegan. On the eastern flank, the plan was to seize the Drama–Komotini railway, an objective assigned to the Bulgarian Second Army and the 10th Aegean Division. 

Greece lost this clash. Because of the refusal to continue defending the territories acquired in the Second Balkan War, a coup took place in Greece and the government of the time was overthrown. A year later, Greece entered the war. Greece eventually recovered its lost territories at the end of the First World War.