On this day in 1917, King Constantine I of Greece, the foremost champion of Greek neutrality during World War I, abdicates his throne in the face of pressure from Britain and France and internal opponents—most notably Prime Minister Eleutherios Venizelos—who favored Greece's entrance into the war on the side of the Allies.
As crown prince during the Balkan Wars of 1912-13, Constantine had led Greek troops to victory on the battlefield; he ascended to the throne in March 1913 upon the death of his father, George I. Educated in Germany and married to Sophia, a sister of Kaiser Wilhelm II, Constantine was naturally sympathetic to the Central Powers after the outbreak of World War I in the summer of 1914. For this reason, Constantine refused to honor Greece's obligation to support Serbia—its ally during both Balkan Wars—when the latter country was attacked by Bulgaria in 1914. Constantine's position was complicated, however, as Venizelos, along with the majority of the Greek government, was determinedly pro-Ally, and the British and French navies held an unwavering dominance over the Mediterranean Sea.
Despite dedicated efforts by the British and French to woo Greece with promises of territorial gains in Turkey, Constantine maintained a position of neutrality for his country. He did allow British and French forces to disembark at Salonika as part of an operation planned in late 1914 to aid Serbia against Austro-Hungarian and Bulgarian forces. By the time the Allied forces were ready, however, Serbia had fallen and the Central Powers drew closer to the Greek border.
By the end of 1915, Allied operations had bogged down in Salonika and failed spectacularly in the Dardanelles, and Constantine was understandably even less inclined to support the Entente. As the British cabinet was told at the time, "His Majesty's decided opinion was that Germany was winning on all points, and that there were only two possible endings to European war, either that Germany would be entirely victorious or that the war would end in a stalemate largely in favor of Germany."
In this position, Constantine was undermined by the charismatic and ambitious Venizelos, who led the movement in favor of joining the war on the side of the Entente in the name of building a more powerful Greek nation. Constantine dismissed Venizelos in October 1915; the ex-prime minister subsequently received Allied recognition of a provisional Greek government, under Venizelos' control, in Thessalonica in 1916. Meanwhile, civil war threatened in Greece, and Constantine desperately sought promises of naval, military and financial assistance from Germany, which he did not receive.
By the summer of 1917, the Allies had lost their patience with Constantine. On June 11, they sent an ultimatum to Athens, demanding the king's abdication. That same day, blatantly disregarding the country's neutrality, British forces blockaded Greece and the French landed their troops at Piraeus, on the Isthmus of Corinth. The following day, Constantine abdicated in favor of his second son, Alexander, who reinstated Venizelos as prime minister. On July 2, 1916, Greece declared war on the Central Powers. Over the next 18 months, some 5,000 Greek soldiers would die on the battlefields of World War I.