The Noemvriana (, "November Events") of November–December 1916, or the Greek Vespers, was a political dispute, which led to an armed confrontation in Athens between the royalist government of Greece and the forces of the Allies over the issue of Greece's neutrality during World War I.
Friction existed between the two sides from the beginning of World War I. The unconditional surrender of the border fortress of Rupel, in May 1916, to the Central Powers' forces, mainly composed of Bulgarian troops, was the first event that led to Noemvriana. The Allies feared the possibility of a secret pact between the Greek royalist government and the Central Powers. Such an alliance would endanger the Allied army in Macedonia bivouacking around Thessalonica since the end of 1915. Intensive diplomatic negotiations between King Constantine and Allied diplomats took place throughout the summer. The king wanted Greece to maintain her neutrality, a position that would favor the Central Powers plans in the Balkans. While the Allies wanted demobilization of the Greek army and the surrender of war materiel equivalent to what was lost at Fort Rupel as a guarantee of Greece's neutrality. By the end of the summer of 1916, the failure of negotiations, along with Bulgarian army's advance in eastern Macedonia and the Greek government's orders for the Greek army not to offer resistance, led to a military coup by Venizelist military officers in Thessaloniki with the support of the Allies. The former Prime Minister Eleftherios Venizelos, who from the very beginning supported the Allies, established a provisional government in northern Greece. He began forming an army to liberate areas lost to Bulgaria, but this effectively split Greece into two entities.
The inclusion of the Greek army along with Allied forces, as well as the division of Greece, sparked several anti-Allied demonstrations in Athens. In late October, a secret agreement was reached between the king and the Allied diplomats. The pressure from the military advisers forced the king to abandon this agreement. In an attempt to enforce their demands, the Allies landed a small contingent in Athens on . However, it met organized resistance and an armed confrontation took place until a compromise was reached at the end of the day. The day after the Allied contingent evacuated from Athens, a royalist mob began rioting throughout the city, targeting supporters of Venizelos. The rioting continued for three days, and the incident became known as the Noemvriana in Greece, which in the Old Style calendar occurred during the month of November. The incident drove a deep wedge between the Venizelists and the royalists, bringing closer what would become known as the National Schism.
Following Noemvriana, the Allies, determined to remove King Constantine, established a naval blockade to isolate areas which supported the king. After the resignation of the king on 15 June 1917, Greece unified under a new king Alexander Constantine's son and the leadership of Eleftherios Venizelos, joined World War I on the side of the Allies. By 1918, the mobilized Greek army provided the numerical superiority the Allies needed on the Macedonian front. The Allied army shortly thereafter defeated the Central Powers forces in the Balkans followed by the liberation of Serbia and the conclusion of the First World War.