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| 1913 | Constantine I Alliance |  |
| 19th May Greece and Serbia signed a treaty of mutual defence against an attack, a mutual border is agreed between the two and an agreement for mutual diplomatic support |
| June Dodecanese Romania, Greece, Montenegro, and Turkey immediately side with Serbia and declares war on Bulgaria, which found itself completely isolated |
| 1913 | Constantine I Balkan League | |
| 19th May Greece and Serbia signed a treaty of mutual defence against an attack, a mutual border is agreed between the two and an agreement for mutual diplomatic support |
| 1913 | Constantine I Battle of Doiran | |
| June Doiran The Greeks defeat the Bulgarian army in the battles of Doiran and Mt. Beles before themselves being defeated at the Kresna straights |
| 1913 | Constantine I Battle of Kilkis Lahanas | |
| 19th May Kilkis Lahanas The Greek army counterattacks and defeats the Bulgarians at Kilkis-Lahanas |
| 1913 | Constantine I Battle of Kresna | |
| June Kresna The Greeks defeat the Bulgarian army in the battles of Doiran and Mt. Beles before themselves being defeated at the Kresna straights |
| 1913 | Constantine I Battle of Mount Beles | |
| June Mount Beles The Greeks defeat the Bulgarian army in the battles of Doiran and Mt. Beles before themselves being defeated at the Kresna straights |
| 1913 | Constantine I Declaration of War | |
| June Dodecanese Romania, Greece, Montenegro, and Turkey immediately side with Serbia and declares war on Bulgaria, which found itself completely isolated |
| 1913 | Constantine I Peace | |
| June Kresna The Greeks offered a ceasefire and the Bulgarians accept due to the danger posed by the Romanian army in the north |
| 1913 | Constantine I Rule of Crete | |
| June Crete Crete and Salonika were definitively assigned to Greece |
| 1913 | Constantine I Rule of Dodecanese | |
| June Dodecanese Greece protested Italy's annexation of the Dodecanese |
| 1913 | Constantine I Rule of Salonika | |
| June Salonika Crete and Salonika were definitively assigned to Greece |
| 1913 | Constantine I Siege of Serres | |
| June Serres the Greek army does not enter the city of Serres in time to prevent it being razed by irregular Bulgarian units |
