the Macedonian region – today, South Kosovo. Bulgaria took what is now Blagoevgrad Province from the Salonica Vilayet. This was followed by massive population movements. Thousands of Macedonian Bulgarians fled to Bulgaria. World War I and National Schism Venizelos was in support of the Allies and wanted Greece to join the war on their side, while the pro-German King wanted Greece to remain neutral, which would favor the plans of the Central Powers. The disagreement had wider implications, since it would also affect the character and role of the king in the state. The unconstitutional dismissal of Venizelos by the King resulted in a deep personal rift between the two and in subsequent events their followers divided into two radically opposed political camps affecting the wider Greek society. With the landing of Allied forces in Thessaloniki with Venizelos' permission and the unconditional surrender by the King of a military fort in Macedonia to German-Bulgarian forces, the disagreement of the two men started to take the form of civil war. In August 1916, followers of Venizelos set up a provisional state in Northern Greece with Entente support with the aim of reclaiming the lost regions in Macedonia, effectively splitting Greece into two entities. After intense diplomatic negotiations and an armed confrontation in Athens between Entente and royalist forces (an incident known as Noemvriana) the king abdicated, and his second son Alexander took his place. Venizelos returned to Athens on 29 May 1917 and Greece, now unified, officially joined the war on the side of the Allies, emerging victorious and securing new territory by the Treaty of Sèvres. Treaty of Lausanne (1923) The Treaty of Lausanne (1923) put an end to the traditional Greek policy of the "Great Idea". This allowed the Greek governments of the inter-war years to turn their attention to the country's domestic affairs and to the building of the modern Greek state. The population exchanges among Greece, Turkey, and Bulgaria after 1923 resulted in the replacement by Greek refugees from Asia Minor of most of the Slavic and Turkish elements in Macedonia. Macedonia experienced a radical demographic transformation with the arrival of the Greek refugees; the Greeks, who had been the 43% in 1913, were estimated to constitute 89% of the population of Macedonia by 1928. Bulgarian relations with Yugoslavia (before 1929 the Kingdom of Serbs, Croats and Slovenes) remained strained over the Macedonian question. Frontier incidents were