The Greco-Turkish War of 1919-1922 was fought between Greece and the Turkish National Movement during the partitioning of the Ottoman Empire after World War I between May 1919 and October 1922. It is known as the Western Front  of the Turkish War of Independence in Turkey and the Asia Minor Campaign  or the Asia Minor Catastrophe  in Greece. The Greek campaign was launched primarily because the western Allies, particularly British Prime Minister David Lloyd George, had promised Greece territorial gains at the expense of the Ottoman Empire, recently defeated in World War I. The armed conflict started when the Greek forces landed in Smyrna , on 15 May 1919. They advanced inland and took control of the western and northwestern part of Anatolia, including the cities of Manisa, Balıkesir, Aydın, Kütahya, Bursa and Eskişehir. Their advance was checked at the Battle of Sakarya in 1921 by forces of the Turkish national movement. The Greek front collapsed with the Turkish counter-attack in August 1922, and the war effectively ended with the recapture of Smyrna by the Turkish forces and the Great Fire of Smyrna. As a result, the Greek government accepted the demands of the Turkish national movement and returned to its pre-war borders, thus leaving East Thrace and Western Anatolia to Turkey. The Allies abandoned the Treaty of Sèvres to negotiate a new treaty at Lausanne with the Turkish National Movement. The Treaty of Lausanne recognized the independence of the Republic of Turkey and its sovereignty over Asia Minor, Constantinople, and Eastern Thrace. Greek and Turkish governments agreed to engage in a population exchange.
Question: How many years was the Greco-Turkish War?
Answer: 4